Number of supported architectures. You'd be surprised for how many chips gcc (or any free compiler) just isn't available. But every chip vendor will sell you a

Number of supported architectures. You'd be surprised for how many chips gcc (or any free compiler) just isn't available. But every chip vendor will sell you a commercial bundle of IDE (most often eclipse...) + commercial compiler + their proprietary embedded OS for a few hundred or thousand dollars. This will most often produce usable code out of the box, without you having to mess around (too much) with linker scripts, startup code and other things a lot of embedded developers have a hard time to get it running. Yes, the licensing is a pain in the butt, but if you get to start working on the actual code you are paid to develop a months earlier the $1000 spent are a bargain! This could of course be remedied by more prople working on gcc (or any other free compiler). But as the majority of a compilers' users will not be willing to invest time to work on the compiler (because they get paid to ship their product), and frankly most of them will not be good in compiler writing. So a commercial company will invest a few man-months of their own, add support for some obscure chip in their proprietary line of compilers, and sell it for $1000/install to the few hundred people working in the (huge) closed source industry building control-systems for power-plants, motor-controls, cheap-IoT-remote-controlled-powerstrips, ...