Operators run a business, it would be ill advised for them to run away with user funds even if users leave their outputs to expire. Of course there are plenty of mitigations for this but it's not a dealbreaker.
Discussion
Cashu mints run a business too, but reputation usually begets KYC, and dark markets beget rug pulls.
The best argument I read so far is that some ASPs could offer longer expiration periods with higher transaction fees, and users can use that for long term savings.