There are often licensing issues (e.g. with third-party libraries) that make it more trouble than it's worth for those companies. Not to mention proprietary to

There are often licensing issues (e.g. with third-party libraries) that make it more trouble than it's worth for those companies. Not to mention proprietary tools required for building, pipeline, etc. -- that is, IF they still can locate the source and IF it's even possible to build it other than in the special "build machine" they used to use.