The CPU makers are willing to subsidize compiler writing in a captive division, but not independent makers.

This is actually fine. These are market forces. These captured companies divest themselves of CPU support other than their new parents quite quickly. Metrowerks actually dropped non-PowerPC support before being bought by Freescale, perhaps to make themselves more attractive to Freescale.

Judging by the track record, Keil will drop non-arm support sooner or later, my bet is sooner.