Alright some evidence, 3 of the top 10 servers are all 1.7.10 (accept a lowest version of it), badlion, cosmicpvp and the hive. 1/3 of the top Minecraft servers are 1.7 and they seem do be doing just fine. There is only one server in the top 10 that only allows clients 1.9+ which is FunCraft, a french server (their website is in french) who seems to be copying everyone else. Every other server on said list supports 1.8.
Minigames aren't necessarily supposed to be competitive they still can be, even you before suggested making a ranked eggwars gamemode (could have been different name). Also 1.7's better hit registration makes the game more fun. Minigames are meant to be fun so 1.7 fulfills that aspect.
More features are nice but the staff may not even include the new features. the main gamemodes on CubeCraft are eggwars and skywars (maybe bingo) how can we tie in curse of binding books into any of those? I guess tridents could find a place in the eggwars shop and skywars loot table but overall most of the features are either not going to change the game much or even entirely change the game around, which isn't necessarily wanted. There is a counterargument that these new features could help make more games but that would require staff to first update to the newer versions and create a game, linearly thinking double the work.
Aside from hypixel and their Chinese hosted counterpart, CubeCraft is #3 most popular server at the moment of writing this, so basically #2... CubeCraft could probably change something about mojang, they are the right size.