Thing is, if the players understand you end up having to add more monsters because of optimising, they soon realise optimising too much becomes a vicious circle/self defeating ... and they DO change their playing style. Or perhaps it is more accurate to say that they will optimise differently - up to the point that the DM doesnt feel like he has to add more monsters to keep things challenging. In either case, you get a better game once players understand they cant really "win" an arms race against the monsters... the DM is flexible, unlike a computer game.
I don't think most people are this smart or this cunning. Many players take the best options they can find. It's human nature. People are competitive. Not every player is that way, but many are. A DM gets a tough encounter wiped out by the PCs in short order. It happens. The DM then starts thinking that the PCs are too OP and then starts upping his encounters.
The issue, IMO, isn't merely that the PCs are too optimized. Part of the issue is the synergy and experience. Players play the same PCs for months, sometimes years. They have, through experience, discovered what works best and what does not work well. They have learned the ins and outs of the other PCs, so they know how to set up advantageous situations.
DMs, on the other hand, often have new encounters fresh out of the box. By the time that the DM learns that having the Orcs move to the outer edge of the front rank so that the NPC spell casters can cast a cone spell, the encounter is already over. Unlike the players whose PCs might be literally more than a hundred fights each, the DMs NPCs and monster combos tend to be in one fight each. Sure, the DM learns certain strategies, but the DM needs to literally learn and eventually know several dozen different strategies for different monster combos whereas the PCs only need to learn maybe 6 or 8 each.
Yeah, playing a PC spellcaster ups the number of tactics that one or more players has to learn, but it is often the case of players who play spellcasters that they are really into their PC. They want a lot of options and thrive on a lot of options, so learning more tactics is fun for them. I have seen this in my game. Once in a while, a player comes to the start of a session and when an encounter starts, s/he suggests that some other PC do something to set up a new spell idea. If it works well, then it starts getting used more often. If it is only ok, it may or may not be used again.
As an example, the player of the Bard was dying to cast Silence. When the chance finally occurred and she found out that the enemy Cleric could just walk out of the area, she was very disappointed. However, she has since cast Silence several times, but very few times in combat. She has discovered that Silence is only situationally useful in combat. A DM running a monster for the first time is often like this player. He discovers that the cool idea that he had for monster synergy just doesn't work as well as he thought it would. He discovers this the hard way, during his first use of that monster in an encounter. Granted, he now knows and he can use the same type of monster again in the future, but that may or may not be applicable to his campaign.
Bottom line, I think that players learn how to work better as a team faster and more effectively than the DM learns, and this is one reason why they start wading through encounters like a hot knife through butter.
I have players at my table that are so competitive that if I throw more monsters at them, they do not learn to dial the minmaxing into a different direction like you suggest, instead they say "Ha! More XP for us.". I just threw an "ambushing assassination squad" at the PC as they were traveling down a road that came within a hair of two PC deaths and my expectation is that the first thing they will probably do when we play tomorrow is change how they spread out and their marching order when traveling down a road from now on (a player has already Emailed the group asking what can be done). Throwing a deadly encounter at them doesn't get them changing the direction of their optimizing so that it is less obvious, it changes their tactics.
