Questions about MTT play.

I play MTT fairly often. I try and play TAG, which seems to keep me going pretty well. But I notice that there is always a player with an enormous stack, say 5x the avg stack. How are these type of players betting? Are they just rotating maniacs on a streak? I just can't fathom a player getting that many great hands with so much action to boot. For example a chip leader with 16,000 chips and the avg being 3,000.
Also it seems to me that TAG works great to get close to the money but I always seem to lose to a clearly inferior hand. (AK vs A6 or KK vs 77). Basically, I am asking what am I doing wrong. I can regularly place in top 15-20%, but can't seem to find the deep money. I am willing to go out on the button but only with top 5 hands. And they fail me more often than not.

Going deep regularly often requires a slightly more laggy style...but not crazy laggy.

This is not to say you cant go deep with TAG...because you can.

Basically what it boils down to is that with TAG you become slightly card dependent to go deep, where with a tad more LAGGY style you favour a slight player dependency...ie you depend on other players being tight. This oversimplifies it, but I'm sure you get the logic.

What this further means is that TAG is usually the way to go in loose tourneys (eg freerolls) or loose tables, and LAGGY is usually the way to go in tighter tourneys or tables.

Try Adaptable, Observant, Aggressive with a bag full of patience, 2 bags full of random kamikaziness, 6 bags full of focus, and a partridge in a pear tree.

What Welly said

MTTs have a rhythm and it's dependant on the size of the blinds, the proximity of the money, the players at the table and a bunch of other context specific things. Getting a decent stack means finding the right style for the rhythm of the tourney. The underpinning strategy is TAG, but building a stack without being dependant entirely on cards requires focussed play with all sorts of hands. This doesn't mean playing garbage for it's own sake but picking spots with wonderful implied odds or identifying players who have very predictable and weak betting patterns to give you chips.

That said, your initial question was about the guys with the big stacks early, they are more often than not lucky maniacs at the happy end of the bell curve for once. Occassionally it will be a decent player on a run, but more often than not the chip leaders early manage to blow it as quickly as they built it.

This article might help you:

https://www.cardschat.com/mtt-guide.php