The only true reason is obviously too little RAM compared to competitors: if ports didn't need major rewrites, just a few hundreds k sales could already justify them.
BTW, Ninty didn't even need 8GB: using a much lighter OS than competitors, 4GB main RAM + 1GB for graphics would have been enough to port many games unchanged and the others just downgrading graphics a bit, but still keeping them above 7th gen.
Online services can't be a reason, as on PC they are totally on the publisher's shoulders, so even the little added services offered by Ninty are more, and free online is a bonus that Ninty now shares only with PC, even more a reason why little RAM can be the only real culprit.