Actually, a lot of people with a lot of sense do pick those first three because it's the character they want to play. If this were a game just of tabletop miniature mechanics, then those first three can be pretty easily dominated by judicious selection from the later ones. But it's not. People play fighters because they want to play fighters, not just because they can tweak the DPS really high. People play wizards because they want to play wizards, not just because they can pump their save DCs high enough to drive some encounter-ending spells. And, believe it or not, people actually play bards and monks. Shocking, I know, to certain viewpoints that choose not to see past the numbers, past the worst-case scenarios, and past the optimization guides.
That was true, for the first little while in our group. I think we went through a couple of "phases" with 3e/3.5e. At first we just wanted to try things out. We played whatever classes interested us. We tried to make a powerful monk and a powerful fighter because they sounded cool.
But our game sessions tend to be 5 hours long. In that 5 hours, we should expect a good 3-4 hours of it to be combat. We go through a lot of dungeons, purchased adventures, and when a couple of our DMs come up with adventures they write them in the same vein(Combat encounter, 30 minutes of roleplaying, combat encounter, 15 minutes of roleplaying, and so on).
Since there was such a focus on combat, being bad at combat meant sitting around for the hour that each battle took watching your entire party be way better at defeating the monsters than you were. Then bragging about it: "Did you see how I took that Dragon down in ONE round because I cast 2 spells at it? That was awesome!" And at first we high fived each other and agreed that is was awesome, since we defeated the dragon. But over time, we became less and less enthusiastic about how awesome certain members of our party were and more obsessed with trying to do awesome things with our own characters to match them.
It was still cool to roleplay our characters. I played an awesome Monk with a cool personality once or twice. But it was 15 minutes of saying "I am very honorable and know powerful martial arts. Fear me." followed by an hour and a half of missing every enemy I attacked. Our group referred to flurry of blows as "flurry of misses".
Then we entered the second phase where everyone started changing characters nearly every session because they didn't enjoy combat with their character or they simply wanted to see how something else did. My group loved character creation more than they did actually playing the game. So, if they could have their character leave the group after every session and get a chance to make a new character, they'd take it.
We played so many different types of characters that we started to learn what worked and what didn't. We realized that single class characters were a fools game. Thus, we entered the 3rd phase: Only multiclass characters and casters.
Most of the worse abuses of the game were kept at bay by the DMs. Most of them relied on...shady wording of the rules. Not necessarily breaking the rules but stretching them. For instance, Pun Pun required you play a Kobold(which wasn't on our list of allowed races) and the DM has to let you change into a creature that's been extinct for 1000 years and exists only in the Forgotten Realms. Hulking Hurler builds required that your DM use the optional throwing table from the one book which was clearly broken and not intended to be combined with Hulking Hurler. We didn't allow stretching the rules. But if you were broken with a perfectly valid reading of the rules, then it was perfectly ok. No one would tell you what you couldn't play.
This is the phase we ended in. Characters included the Fighter/Barbarian/Frenzied Berzerker who could pounce on a charge and averaged about 150 points of damage a round. Which was more then the hitpoints of nearly every monster whose CR was even close to his level. Another character was a combination of Warlock and some other classes who could hide in plain sight, had permanent fire whips in both hands that did 10d6 damage each with 5 attacks per round and could sneak attack with all of his attacks while adding warlock's blast damage to them.
One of the players from that game joined someone else's 3.5e game(when they got bored of 4e) and is apparently being forced by the DM every session to roll up a new character because each character he comes up with is way more powerful than the rest of the group. But no matter how hard he tries, the next character he comes up with is just as bad. He can no longer think in terms of "bad" characters.
Now, I understand that some groups who either don't play as often as we do(We were playing 3-4 times a week) or have less combat encounters might still be playing in phase 1. But that doesn't mean that once you know how the system works that our actions aren't the logical conclusion. I was one of the only people left in my group at the end who even considered playing a single class character at the end for roleplaying reasons.
EDIT: I think it does take "work" to break it. But the work isn't that hard. And once your know a couple of ways of breaking it, you tend to think in terms of what's broken rather than what's balanced. It didn't take that much work for one of our PCs to come up with a character. Normally a new book would come out and they'd immediately say "Did you see this feat? Doesn't that make anyone who is a shapechanging Druid SUPER BROKEN? I'm making up a Druid for next week."
Since no one us were char op types at all, and since I don't enjoy doing that, the alternative was to stumble along patching it (which I also don't like), or dig up why it was broken--AKA work. 
