A few things you got wrong about ETH staking:

. As of today, you can get much better yield than 4.1 from different services (actually close to 8 on some, and close to 5 on some very trusted ones (DYOR))

. Even if they all tend to converge to 4-5ish yield, that was not the case before last Ethereum upgrade. So, many people have been staking for a long time and simply decided to leave their money, since they get a decent average yield over years.

. The thing about "people not being able to unstake" and "being prisoner" is slightly exaggerated. Some services started giving you usable rewards on a daily basis months before the last upgrade (without unstaking). And some allowed you to unstake as well, especially for people who don't have 32 ETH.

Otherwise, your question on Bitcoin is a bit biased. I'm stuck on the words "centralized custodian" that, in my mind, refer to banks, KYC, constraints, and BS. Considering this, I wouldn't stake my BTC, just for privacy sake.

Problem is that there is very little DeFi culture in Bitcoin world. If there were something similar to DeFi on Ethereum, with fully audited staking dApps that don't even know your email address, I would consider staking above 5%.