Vs you have bitcoin, you want to erase the public trail so you convert to XMR, then send XMR to a new anonymous exchange and convert to Bitcoin. That seems more simple, convenient, and surefire.
Anonymous exchange?Can you mention a few "anonymous exchanges",which are totally anonymous and accepting monero transactions?I don't know about any anonymous exchanges.
BTC mixers are more popular,because most of the crypto users want to deal with Bitcoin rather than Monero.
BTC is accepted almost everywhere in the crypto industry,while Monero is accepted in only a few places on the clean web.I'm not talking about the darkweb,where Monero is the main cryptocurrency.
I don't think that anybody is recommending BTC mixers over Monero.Both options are risky and there's no way to achieve complete 100% privacy.