I made the same complaint in a previous "someone just rediscovered Ada" quarterly thread, and an Adacore dev replied that most of their lib are now GPL + linking exception (well, he didn't say "now", but on their former Web site it's pretty clear no exception was mentioned anywhere regarding their OSS code, so I assume there was a change recently).
I agree with your sentiment in that, Adacore being into high end consulting, I don't see what they'd be losing by relaxing their licencing. This would bring in new people (I mean, if there's a new "hey I just found out about that Ada thing" thread popping up every few months here or on Reddit, clearly the language has something going for itself), which is clearly something they want to see happen.