I think one of the main reasons mega walls has a lower playerbase than other hypixel games is the youtubers. Many youtubers from 30k to 500k subs playing games like skywars and bedwars whereas there are very few youtubers with above even 10k subs making mega walls or blitz videos. Technoblade used to play mega walls and blitz but there videos are now extremely rare on channel. Lego maestro (ik cringe) now hardly ever uploads megawalls. I think that this is actually a key role in why sky wars and bed wars have the largest player base on the server.