Are you mayhap mixing up polearms and staffs?
Not that I was aware of staffs being DEX weapons ...
Possibly but I can tell you for sure I've never been at a table with a Brabarian or Fighter or any other STR focused class that opted to use a polearm. As far as I can tell polearms are largely dead weapons.
There are no dedicated DEX melee weapons in 5E. Finesse weapons use DEX or STR, whichever is higher. Monks can use DEX on any weapon considered a monk weapon, which includes quarterstaffs.
And polearms are considered the go-to meta build choice for martial classes in 5E.
