And that's the main problem. Today's designers don't differentiate between websites and "serious" applications.
A website must be easy to navigate without any training because it's one of several hundred that the user visits each week. Any learnings are forgotten anyway on the next visit. So it has to be completely self-explanatory.
A "serious" application on the other side is used for several hours every day. Efficiency beats simplicity in that case because that three-day crash course a user might need in the beginning is neglectable in comparison to just five minutes of saved time per session on later use.
But most UX designers these days only seem to know casual, consumer-oriented - and then try to apply the same recipes to enterprise apps. It's almost always a disaster.