My theory on Melee...

[Amechra]

... is that it doesn't combo well.

For example, look at spellcasting; there, if you want anything complicated, you can stack a ton of feats and spells together to pull off crazy things.

Melee, well... you can grab extra damage? And reach, I guess?

When you are a looking through spells, you can usually find a spell or two that makes you go "well, i can mix this with that, and kick ass."

When was the last time you did that with a non-Homebrew martial class, or group of feats intended for a martial character? Probably not too recently.

[Jackinthegreen]

As far as pure martial melee goes, it generally goes into the feats improved Trip, Knock-down, Power Attack, Improved Bull Rush, Shock trooper, and Knockback.  Besides the damage, it also moves the enemy around as you like (off a wall or cliff is a fun one) and trips them up, which pretty much forces them to take a move action to get up and thus gives you an edge in the action economy.  For extra damage, Dungeoncrasher of course does it well.  This combos with itself a bit, but also works with someone in line to get an AoO, and if that person can also do bull rushes at will on attacks then they can play ping pong until the target dies.

Imperious Command just plain shuts things down, and the usual use of demoralize requires being in melee.

The Three Mountains weapon style can be pretty effective since nauseating the target means it can only make a move action and a swift/immediate.  Trip it and it's likely screwed.

If one is fine with cheese, the Aptitude weapon Boomerang Daze shtick is another fun one.  Since the fort DC is based on damage done, improving damage increases the chance the target will fail while simultaneously bringing them closer to death anyway.  Daze takes away actions, and if the target can't act then it's dead.

There are some other "melee" combos though such as the de-buffer, which combos with anything save-or-die.

[Unbeliever]

What is there's just less of it? 

If you think that it's essentially random whether an ability is good or not, especially in a combo, i.e., that game designers don't really think about these things that deeply when they are writing them.  Then, it's really just luck of the draw. 

There are a lot more spells in D&D than there are anything else -- a lot more spells than feats and class abilities especially.  So, you're more likely to get "winners" that way. 

I also think that designers seemed to be oddly less tepid or cowardly when it came to spells.  For some reason they were often incredibly afraid of adding something cool or interesting to a class.  They spent a lot of effort balancing it against other things or turning it into 5/10 spellcasting or loading it up with (arguably) thematically appropriate abilities that were really useless or nearly so.

Spells, on the other hand, they just seemed willing to go bonkers with a lot of the time. 

[Zionpopsickle]

... is that it doesn't combo well.

For example, look at spellcasting; there, if you want anything complicated, you can stack a ton of feats and spells together to pull off crazy things.

Melee, well... you can grab extra damage? And reach, I guess?

When you are a looking through spells, you can usually find a spell or two that makes you go "well, i can mix this with that, and kick ass."

When was the last time you did that with a non-Homebrew martial class, or group of feats intended for a martial character? Probably not too recently.

Melee actually combos very well in that the pieces that are supposed to fit together tend to.  The problem is that it doesn't synergize nearly as well as magic.  Solid fog+evard's tentacle rape aren't actually a combo that is built into any progression, they are just two spells that when combined tend to end fights against certain types of enemies.

I think the biggest problem with melee is that it is poorly focused.  Too many feats and abilities make you better at killing mooks, which you are already great at and the mooks tend to contribute the least to any battle anyway.  Spells tend to deal with mooks as a side effect of doing what they are supposed to do.  Stinking cloud ruins mooks but really you are casting it for other reasons than just shutting down mooks.

[Amechra]

Crap, I actually meant synergize;

But yeah, the fact that Melee is kinda more focused on getting rid of mooks or stuff that require a lot of room...

[zook1shoe]

Aptitude increases what a melee person can do, as mentioned above.

I'm partial to lots of tactical and weapon style feats with it

[RobbyPants]

But yeah, the fact that Melee is kinda more focused on getting rid of mooks or stuff that require a lot of room...

Only within reach, which you usually need magic or something esoteric to improve beyond ten feet.

This brings up range. Casters can typically do great and wonderful things at distances measured in hundreds of feet. Some of their spells can probably reach out further than they can actually spot things, if they're forced to roll for that. Melee has a big problem with maneuverability. They have to actually get to their target to be able to affect it, and many targets have faster movement speeds and/or more options when it comes to moving.

So, even if you make a really cool combo, you still might not get a chance to actually use it.

[Endarire]

Hood.

Really.