They could choose to support just one or a few of the distributions, but this decreases the potential market and again decreases the incentive to port to Linux. History provides the lesson. Fragmentation among the various proprietary flavors of Unix hindered development of desktop applications for Unix. This, combined with the high cost of Unix workstations, pretty much eliminated Unix as a contender for the desktop. Linux plus faster and cheaper PCs has solved the cost problem.
Standardization is meant to address the fragmentation problem.
The implicit assumption here is that proprietary software running on Linux is a good thing. This is not a universally held view and a certain open-source leader has been quite vocal about it. Then we'll look at some of the newer standards efforts that are underway. Before Unix standards got any sort of official status there were de facto standards. This API provided a means for application programs to utilize system services in a well defined way, services like file access, memory management, and process management.