Polearms are one the most used weapons in DnD 5e. Polearm Mastery is one of the best feats a martial class can pick.
I have never seen a STR focused build use polearms...ever. Barbarians gravitate towards axes, fighters towards swords, etc. What I have not seen is a STR focused class use polearms.
I have never seen a DEX focused build use two-handed polearms...ever. Fighters that don't use shields often use polearms because they don't usually have another use for their BA, and Polearm Mastery gives you a bonus action butt-of-polearm attack that deals 1d4+STR damage. (You can also use GWM with two-handed polearms).
Rules-wise: Polearms are defined as the glaive, halberd, quarterstaff, or spear. None of those weapons have the Finesse trait, and thus none can natively be used with Dex. The only exception is that monks can use quarterstaves and spears with Dex because those are Monk Weapons.
