Why not use drivechains on BTC today? Because you need to change its software! And I don't agree that drivechains are needed on Bitcoin. So even if drivechains are done in a soft fork you add complexity, which I am against. I want Bitcoin to be an immutable store of value and excel at it and nothing else.
You can use other networks today and you even can easily fund it with your BTC (think of it like an investment in stocks). Once you got the value you looked for from your use case transfer back those leftover back to Bitcoin.
Ethereum is miles ahead when it comes to "drivechain" solutions. Every network other than Bitcoin and Monero offer certain smart token capabilities. Even BCH has "cash tokens".
Taproot had unintended consequences. If you add more complexity and you unknowingly (at first) might kill its most valued qualities.