If you can’t afford 400g flasks you don’t get invited to raid, so you go to a worse raid who may not clear every boss, and those raids have more undergeared people in them which increases loot competition. So buy not RMT’ing you are missing out on loot. You also get to do more raids since they are faster.
Raiding itself is the inheritent driver of RMT, not the loot system and anyone being honest knows this.