If ppl prefer to use Bitcoin because it's decentralised why can't it be updated in future to obfuscate spends. It's still going to be decentralised.
There's mixing. It's possible to create a second layer, like LN, than automatically mixes coins.
Bitcoin can be improved when it comes to privacy, but why should it be? I own some old bitcoin that was bought long ago on a now defunct exchange. Nobody can subpoena that exchange as it shut down years ago and the owner was found dead years later. If I paid you for something illegal, nobody would be able to find my name, or even the person who bought bitcoin from me. Bitcoin is as private as we want it to be. If you use a centralized exchange that has all your private data, with pictures, you have no privacy, but some people don't care.