Many people do not find attractive neither the loot nor the gold that these treasure rooms provide, for this reason nobody is interested in killing the mini or opening the chests, and what if the mini boss is allowed to drop 5 phantoms tokens. I think this is enough motivation for players to do treasure rooms, let me know in the comments what you think.

Phantom token return rate: 15 tokens per run.
Runs needed to have 50 tokens and buy catacomb's key recipe: 3 - 4 runs