Well polearms are obviously OP and the vast majority of players know it.
The average game as 60-70% polearm users.
Lots of people use polearms because there is a huge fucking variety of weapons and playstyles for 1 class of weapon. You can spear+shield, pole on horseback, use long 2h spears, use long ass glavies and ninja shit, use short blunt weapons, use axes, pikes for horses.
It's probably the most variety out of all of the weapon choices, and a lot of people that don't already have a build in mind go for it. It's a very safe choice for new people too. That is a large factor into why you see so many used.
Back in the day, it was clear some polearms were broken(everyone used a bec de corbin) now you see a pretty good distribution of pole weapons.