"Why can't I pay LN invoices from it"

And of course on a technical level you could, but the UX for that usecase is intentionally shit. Its designed for you to withdraw to self custody. Its two button clicks then copy and paste invoice (or lnurl-withdraw) it doesn't show you a dollar balance for your account and it has a max deposit amount of 250k SATs which they plan to reduce over time until a complete transition to fully self custodial can be made.

To keep this on the topic of culture building, what's the transition plan to fully self custodial look like for e-cash applications? What UX decisions are made to discourage payments for goods and services and to only e-cash in platform until withdrawn?