compression is not free, dictionary compression:

1, complicates and slows down update, which is typically more important in OLTP than OLAP

2, is generally bad for high cardinality columns, which requires tracking cardinality to make decisions, which further complicates things.

lastly, additional operational complexity (like the table maintenance system you described in last paragraph) could reduce system reliability, and they might decide it's not worth the price or against their philosophy.