Imo the game needs more challenging solo content.

Casuals are far more likely to try out gradual difficulty solo content than bother to meet and talk with people to get into a static to do raids, that takes times, mental effort and also requires specific times for raid and organize that many do not like being limited to.

Now they could also make a solo savage raid option where the npcs behave very average or slightly below average so victory COMPLETELY depends on your own PERSONAL performance but that is probably a lot of work instead of some solo designed deep dungeon.