It seems to me that you are wrong in your assessment.
BTC can be converted to other coins inside the Leather wallet.
I went through the wallet but I saw no way I would be able to if I funded the wallet.
This is the main home screen of the wallet:

When I clicked on STX and USDCx, you can see
swap:

Click on bitcoin, you will
not see swap:

STX is the main coin and the only coin when I clicked on swap for general access:

But you can swap to other coins which I called STX tokens but I may not be correct. I think they are STX tokens and some of them are altcoins pegged to bitcoin price:

Wallets like Unstoppable first did not supported swapping to bitcoin, but it supported many chains and their tokens. It was later that it supported swapping to bitcoin as it supported cross chains. But leather only supported STX and no other chains. Although it is not a problem.