Chipmixer is the best Bitcoin mixer but is not the only mixer on Earth.
It depends on what is called best, anything centralized to some people are not seen as the best, Chipmixer is centralized. You are not wrong, Chipmixer is not the only mixer on earth, it is even not only the centralized mixers on earth, but among the centralized mixer, Chipmixer is the best, you are right.
This has been the best guide on this forum about mixing, if I should have to go for the best option, I would prefer to go for converting bitcoin to monero, then converting the monero back to bitcoin on a decentralized exchange like bisq.
Honestly if you use a non custodial wallets and don't have Bitcoin from illegal sources or you don't want to avoid tax ie., you don't have to seriously use mixer service.
Some people are making use of exchanges, they may also due to some privacy reasons prefer to use a mixer before finally moving the bitcoin to a noncustodial wallet. Also it can be used because of some other privacy reasons.