I've been playing with the 3d module in Foundry, and this is the biggest issue for me. How to see thru walls and stuff.....because in a 10 ft wide hall with walls, you can barely see what is happening most of the time.The big problem with these approaches right now is that turn based combat and real time result in different perceptions of our environment. As we go more towards 3D, they begin to incorporate things like blocked sight as LordEntrails mentions .... and that can result in players not seeing something their PC should have seen. It is easier to adjust for a player to pretend they did not see what they did see than to make sure players see what their PC did and they didn't ... because you do not always realize the discrepancy.
I agree those look awesome, but it takes a professional to make maps that look that awesome. Maybe someday AI will be able to do it but we aren't there and I suspect it will be a long time before we are. Then throw in NPCs and monsters which will have to look just as good. For a lot of people, this would be a worse experience than a tabletop. With the standard tabletop experience you let your imagination fill in the visuals like you do with a book.Some times the lines between videogame and VTT will be erasured. With the same software you will can to play a VTT or a standar videogame created thanks the tools of that same software.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.