Now I am NOT saying Mark is slow by any means. I am saying it takes more time^5 to do something cross platform in BMax.
That's rather an assumption. For the most part, cross-platform support isn't that hard to do, and ends up leaving you arguably with better code and what's likely to be an easier to maintain engine in the future.
Windows is probably the hardest environment to support anyway. You've got such as mish-mash of hardware and libraries installed, drivers that lie about capabilities, etc. The only reason it does so well is because of critical mass. How long did it take to add DirectX support to an already adequate OpenGL based system?
On Mac you have everything basically standard. On Linux it's also pretty much the same. Most of the problems with Linux have been down to inexperience on the user's part (not knowing how to download driver install scripts) and no packaging for automated dependency resolution. None of these things have taken BR any longer because they haven't done anything about them.
The other side of things is say BlitzMax no longer supporting cross-platform would cause people like me to leave, and though you might not think I'm that important, other people may have the same idea and then BlitzMax would sell less.
So from a BR perspective, not supporting cross platform, especially when some of their other real competitors do would be a bad idea. Who cares how many games get made? They're trying to sell a compiler here.
Why would you buy a compiler without a built-in 3D engine if you want to do 3D stuff anyway? This is the same old typical whining that's gone on for years here. If BR were to drop Mac and Linux support, you wouldn't get your precious 3D module that much sooner, and they'd lose sales and market share. The other fact is most of you people aren't even going to produce anything saleable with it, so why you're so worried about platform market share is beyond me.