Mason villager nether quartz trade is too rare

Nether Quartz is one of the mason villager's expert trade, but it is really hard to get.
Since there are a total of 32 possible terracotta blocks to choose from, quartz has only 3% chance to be the trade unlocked.
It would make a lot more sense if the terracotta came from a group pool so the chance to get quartz would be 1/3.