The transcript and enhance feature probably work better with lossless, if it record in "compressed" and those features doesn't work great, users might complain.

It might also annoy pro users if it was compressed by default and they didn't realize it and their recordings turn out to be "unusable" quality.

So just record in lossless and most users go on without realizing the storage usage since most user probably don't record much, beside they did mention the "compressed audio" option in the app description on the app store.

You can always "compress" them afterward off device but you can't unlossy uncompress back to the original lossless audio.

PS: I am assuming apple means lossy compression when they say compressed,  the lossless version should also be stored losslessly compressed and not as just raw audio.