No one here is saying that Hide and Seek doesn’t need more maps, but new maps simply have a higher level of quality compared to older maps. Java Hide and Seek used to have more than 20 players (Bedrock has 16 players per game). Hiders already win a majority of the games and some of the mentioned maps (especially Hotel California) are too large for 15 seekers (if seekers even find that many hiders). 
Most game modes are map dependent as each map offers special and unique strategies. Some maps are better for siderushing, while other maps are better for going mid first (SkyWars and TreasureWars), same applies to Murder Mystery where the murderer has different mechanics and tools to use, e.g. invisibility, speed, teleporter, spacesuit to hide the skin etc. The map is often an important part of gameplay, which doesn’t just affect Hide and Seek. ^^