Doesn't have to be "every person and company, in unison, in a grand conspiracy" and other such strawmen.

We could try steelmaning this argument instead: it's enough that most big companies who would otherwise have incentives to contribute.

Before FOSS got in fashion, around the early 2000s, most commercial companies wouldn't touch it as contributors and were openly avert to it, and to open sourcing their stuff. This can be the case again.