No one has suggested that people "expect the same UI between mobile & desktop apps". The point under discussion is that it's desirable for apps to have "cohere

No one has suggested that people "expect the same UI between mobile & desktop apps". The point under discussion is that it's desirable for apps to have "coherence and familiarity" across platforms. It's important that there be coherence and familiarity between Slack and Spotify's mobile, desktop, and web apps, for example, because most of their customers will use at least 2 of the 3 in any given week, which likely contributed to their choice to use Electron for their desktop apps.