Businesses want uniformity and commonality since, in theory, it should lower development costs (see projects like flutter and fuschia, which have the goal to make every platform web based).
The problem is that users/customers have higher expectations for their user experiences than the web can offer on mobile/desktop/etc.
Robinhood, Duolingo, Slack are a few good examples of UX being huge differentiators.
I understand what you are saying but am not clear as to why it should be so. Having programmed GUI apps in Microsoft Windows and X-Windows/Motif (which can be remote) on Unix systems i am not sure why we cannot have a similar uniform architecture for "Web Apps". After all the "Browser" is considered a platform in itself. Also given that HTTP has now been munged into practically being a Transport protocol for anything, previous limitations are no longer an excuse.
The problem is that users/customers have higher expectations for their user experiences than the web can offer on mobile/desktop/etc.
Robinhood, Duolingo, Slack are a few good examples of UX being huge differentiators.