I'm not sure if OP is being sarcastic or not, but in summary, Fighters in particular are weak because feats never were as good as class features, save for a couple which aren't on the Fighter feat list anyway. Feats don't scale, their effects are minor, and much more useful things could be gotten from other classes.
Of course, Fighters aren't all bad. Once you leave core, there are things like the Zhentarim Soldier and various alternate class features and better feats to choose from, so if one makes an effort to it one can make a decent Fighter character1. However, even at the highest point of sourcebook use, there still isn't any reason to be a pure Fighter. You're better off multiclassing because you inevitably run out of feats that are necessary or useful for your character.
1This is in the context of comparing the Fighter to other warrior characters and not to spellcasters or experts, which is a whole other bag of worms
In the end, the Fighter class is a product of its time. They were developing 3.0, when Feats were a new and exciting thing and they vastly overestimated their usefulness. Nowadays we have newer, better-thought-out classes like the Warblade as well as various multiclass builds that let you play your chosen warrior character concept, but to play a pure, unaltered Fighter is just not a good idea. There are better and more fun ways to do it.
