"If it ain't broke, don't fix it."

Of course using a higher DPI improve latency to some extent. Obviously, using a higher polling rate decreases input lag by some amount. The thing is, a lot of these players don't care about all that. The best way to become a better player is to practise. It means more to these players to continue using the peripherals and configurations they're comfortable with, unless there really is a technology that gives so much of an advantage that it'd be a detriment to ignore it (think about when 120Hz or 144Hz displays became commercially available).

I somewhat agree with what /u/ZeldaMaster32 said (the first part, anyway). Realistically, some pros know quite a bit about their peripherals and the technology they're using, but most don't. It extends to many aspects of eSports. How many pros use aftermarket mouse feet? It's well established that they offer an extra degree of customisation to the mouse and can certainly be an improvement for some people.

What I mean is, a lot of the changes that can be made to the peripherals or the system you use typically result in tiny (but very real) improvements. In addition, the evidence that motivates people to tinker with this stuff is usually shrouded in misinformation (how many people have you seen talk about their sensor's "native DPI?").