That argument is a little circular. If a platform has significant market share, apps get ported to that platform. If not, it doesn't matter.

Before there were Web apps, all software makers wrote apps for multiple platforms. Porting to a platform has a cost, but, for a successful software company, not a relatively large cost. Even unprofitable platforms are likely to be supported by some software makers as a way of erecting barriers to entry, or to speculate on the future success of that platform.

Users will expect all the features of their platform to be well-supported in their apps.