@Pasa: I could get on board with that gem idea.
@Digital_Dave: Eh, the problem is that GoW is a strategy game, not a dexterity game. The point is to be able to plan, not to go as long as possible without “crashing.” So it just doesn’t fit the theme when you have a huge random cascade that spoils the 5-match you were trying to set up.
@Razlath: True, it’s often not many extra turns you miss out on, but by the same token, it’s therefore not a big deal to just let us have those extra turns, especially since the announcer is going to say we got them anyway. 
As to why players under 100 play them more, I think it has to do with the relatively low rewards they get from PvP. I mean, no level 100 player can really stand up to the types of teams run by 500+ players, at least no consistently. Thus, their ability to earn gold from PvP is relatively limited, especially since you have to spend money to make money, and in the early levels gold is harder to come by. Thus, TH represents a risk-free way to earn substantial gold regardless of level, which makes it significantly more valuable early on when your gold is tight and your ability to earn it is limited. Plus, anyone under level 100 is also going to want all the other rewards too.
I confess I initially found it mystifying that higher level players consider TH a waste of time (I still find it very lucrative), but then I consider that the real veterans here can easily earn a large chunk of gold in fairly short order because their teams are so much better, it makes sense. At level 500+ with all the really good legendaries and multiple traits, a relatively easy battle is over quickly, and one that takes longer gives more gold, so if you really just want the gold (as you would at that point in the game), it makes sense. I want gold, but I’m also lacking in gems and keys, so it makes sense to me to play TH and get all the above rather than focus just on gold.
In short, I don’t think the popularity of TH is necessarily a response to the “cool” factor; I think it’s actually an eminently rational economic decision given the options.