Mikami deserves the blame for the Nintendo exclusivity deals. That was completely his call (Suicide bombing the franchise with RE4 on that platform was also his call, but that is another topic, and probably beyond redundant at this point).
Giving Capcom AND From Software credit though, these two Japanese companies, are actually doing pretty good at reaching across all platforms these days, especially prioritizing PC gaming, which is great and really smart business practice. Reaching out to as many players as possible is a no-brainer but I guess that wasn't obvious back then. Heck, even today there seems to be a trend towards more exclusivity deals, by and large, but it seems to be much more transactional rather than purposeful.
Regarding RE0, maybe the best way to cope with the story is to just imagine that Rebecca took a nap in the mansion west save room before she pepper sprayed Chris and had a nightmare and that was RE0! "Rebecca's Nightmare" has a nice ring to it, dunnit?