Spoiler: a mix of corporate vanity and to avoid recurring licensing fees, though Arun Venkatesan elaborates a complex trend.
Sadly, much of the justification behind typefaces from some very admirable companies is quite shallow. I can't help but feel that some of these companies wanted a custom typeface simply because that's what everyone else is doing. This cargo cult mentality that is so prevalent in design is at best wasteful and at worst illegal.