What's so bad about SDL anyway?
SDL is a standardised API for accessing graphics, sound and other hardware across many different platforms. It has nothing to do with X11 unless you're talking about it running on Linux.
I'd much rather program for SDL than Picasso96/Cybergraphx and AHI.
You've got to be a bit realistic here, the Amiga market is miniscule compared to the huge amount of platforms SDL works on. SDL opens up ports which we probably never see otherwise.