The problem is that BlitzMax exists in a world completely cut off from mainstream programming. It's been around for a while, but there are still no books on programming with BlitzMax, popular libraries don't offer BlitzMax modules on their sites, and none of this will ever happen. So it's a developmental dead end, and will never be taken seriously or even noticed, even though BMX and its associated libraries are far better than a lot of other languages out there.
another downside of that is the perception that it's just a "toy language" in the minds of others, since they've never heard of it.