I'd recommend some better-known open-source mobile wallet options over this 'Key Wallet'.
Otherwise, there's a pretty comprehensive list by dkbit98 of open-source wallets (although multi-coin)
here.
Sorry, but your recommendation is a bit off‑topic because in the OP it was stated that this thread is open as the response to a user who wanted the simplest wallet possible, without any bells and whistles. I wouldn’t say that the wallet you recommended belongs to that class of wallets.
Why would a wallet remove hardware wallets support?
They’re probably trying to be the simplest wallet in the world, just as you wanted.

On a serious note, a likely reason is simply the lack of development resources.