I'm not a current 3e player, but I was for eight years. So I'll answer.
1. You are absolutely right that the dominant strategy for melee characters was to use feats to create a specialized attack, and then to spam that attack as much as possible.
2. But, combat was short, so the spamming wasn't as noticeable.
3. In that short combat, at least a few rounds were spent getting into position to spam your attack, or moving on to your next foe after spamming your last one.
4. If a combat lasts 5 rounds, and you charge in the first round, full attack in the second, full attack in the third, move and attack in the third (because your foe died), and full attack in the last, did you spam?
Of course, if combat lasts 7 rounds and you, in order, use Charge, Cleave, Crushing Blow, Reaping Strike, Passing Attack, Reaping Strike, Reaping Strike, did you spam? Maybe you did. I don't think so, but see point 6 for more on this.
5. Some people LIKE spamming attacks. Those that didn't played spellcasters.
6. There's a certain sort of person who gets their kicks from describing their attacks. So yes, theyr'e spamming the same thing over and over, but they're describing it differently each time.
In 4e, their attacks have names, and little italicized lines of flavor text, and a certain percentage of the combat-describers seriously believe, and repeatedly claim on this forum, that this kills the roleplay aspect of describing your attacks. They look at 3e with its bull rush and sunder and disarm and whirlwind attack and full attack and see a wealth of roleplay opportunity, and they look at 4e and proclaim that every Reaping Strike is exactly the same and that you're just spamming it like you are on a computer and repeatedly hitting the "Reaping Strike" button. The fact that an individual character has more viable attack options at level 1 than most non-spellcasters in 3e have at level 10 doesn't cross their minds, because, to them, that's just a slightly larger selection of buttons to push, and it can't compare with the infinite ways you can describe a full attack.
In a way, the vanilla, spammable characteristics of 3e non spellcaster combat is an advantage to them- since "full attack" is thematically a big fat nothing, its a canvas onto which they can project anything they like. They can't do this in 4e because their big empty canvas is covered up with a italicized line of text that says something like "You punctuate your scything attacks with wicked jabs and small cutting blows that slip through your enemy’s defenses."