Once you move a pawn, you can't move it back. This creates weaknesses which is what hypermodern openings try to exploit. The nimzo indian defense for example uses the fact that white has already committed pawns on d4 and c4 to prevent an e4 push and eventually playing c5 and d5 at the best time
Is "Hypermodern Chess" Inferior to Classical Chess?

Aye I didn't even consider the Nimzo-Indian or things like that... I guess I am referring to openings that are perhaps a bit more extreme in this idea. Here are some examples of positions I'm referring to:
These kinds of positions seem to give one side a wall of pawns and while it may be ok to play this way I wonder if it's worth the trouble. I tend to have huge problems in playing these positions because I get into bad positions because of the pawn storm or simply not being able to find counterplay. But In classical chess this doesn't seem to be a problem at all except in rare situations.
I didn't really consider openings like the Grunfeld or queen's Indian because pawns are played in the middle of the board pretty early in those openings.

Hypermodern openings such as the Hungarian Opening or Owen's Defense rely on your opponent over-extending his pawn line. If you employ this strategy you are usually more defensive( probable preference to closed games) and are well prepared for the advance. After the initial exchanges that I'd hope are well calculated before hand and perhaps a well timed castle you can seize the initiative while still applying pressure to the center with double fianchettoed bishops or other minor pieces theoretically. In my personal experience I prefer a strong pawn advance from an opponent because of the potential boon a successful capture and opening of the center files can be in some instances but I will always prefer a closed and far more defensive route if possible. The variables are obviously numerous and complex but, playing the flanks and generating play with your knights passed and over extended pawn line is more often than not devastating. On a side note, Prophylactics is a huge part of hypermodern theory and if successful can you shut down, control key squares and dictate the tempo of your opponent, If employed correctly you can tax the other player heavily for certain moves that will allow an opening for him to generate play against you. Keep in mind no strategy is the "end all" in chess but from someone who subscribes to this school of thought outposts, prophylactics and sharp positional defense are key. It's worth developing and looking into a great deal because it was developed much later than classical playing styles and in my opinion was an attempt at an anti-thesis for Classical playing styles which it can be if conditions are right.
From what I can see the point of playing hypermodern chess is to try and control the center with pieces until you can find an advantageous time to occupy it with pawns. However I wonder if this strategy is worth the trouble if there's nothing wrong with classical chess to begin with.
Some of the most popular openings at top levels are all classical like the Ruy Lopez or the Queen's gambit declined. The Reti is played sometimes but the position after 1.Nf3 d5 2.c4 d4, playing in classical style, is supposed to be strong for Black, and only after two moves no less. Maybe this is just a problem with Benoni structures in general... And on the English, Black is really spoiled for choice and can even just play some kind of queen's pawn defense and just be equal.
So I wonder if there's any real point to this other than hoping to get your opponent out of normal openings. Also as an amateur player I find myself losing many games simply because I can't calculate my way out of some pawn storm that the opponent can play without even thinking. I like these kinds of openings because they are a good way to avoid popular theory but if I'm just getting into positions I can't play anyway then there's probably no point in this anyway.
I just don't see much value in it for anyone other than someone who isn't terribad just trying to mix things up.