Plenty of them are still at Blizzard, though OSRS did a good enough job of having new staff and still sticking to the original game's design philosophy. It's really not an issue, it's easy to see the bounds of how the game could expand within the original design philosophy.

For example, no LFG, keep the level cap, no transmog, no multi-server sharding, no removing RPG elements like hunter ammo, things of that sort.