In my experience bitcoin cash is a fork of bitcoin even BCH is faster and cheaper to use due to larger blocks but still it'a seen that most of the people are using BTC than BCH so why is bitcoin doing better than bitcoin cash?
Because any plug is incapable of something more from the original, because the idea is the same and they differ only in the volume of bidding and demand. And the risk of investing in the fork is much higher than in the original. Basically, all forks are suitable for day trading.