Its mainly because no one did any effort to replace DLS. Its in place since early 90s and its known for giving surprises. Cricket is an outdoor game thats constantly interrrupted by events like rain, bad lights etc so we need some kind of support But I have to admit that this DLS has not given any support rather giving confusion.
The thing is that
DLS has actually been effective in producing fair results majority of the time which is why the ICC decided to simply stick with it even though some fans absolutely detest it.
The same is true when it comes to similar mechanisms in other sports like Soccer etc. Am not expecting any major changes to it anytime soon.
If DLS method was able to produce effective results then everyone would have been happy with it and we would not be discussing changing this system.
The problem is that majority of the people agree that DLS does not produce the best results and gives an unfair sort of advantage to one team over the other.