Because the vast majority of Monitor Sales-Volume are (public) tenders from companies buying huge volume, and those companies still mostly look for monitors <4K (without fancy specs and without i.e. USB-C).

If 4K reaches mass-market for those, the specs will shift down and there will be room in the (much smaller) Premium-Tier monitor segment

Heck, even if you just want USB-C and an integrated webcam on an average display, the price-hike compared to one without it is crazy, because everything except those basic office-monitors is still niche-production...