League of Legends (LoL) Question: How come no one use Ohmwrecker?

The people who could build either:
a) Have better items to buy
b) Can't really afford it

The people that belong to the a) group are mostly top laners. Why build Ohmwrecker when you can get a better item like Randuin's Omen or Banshee's Veil etc.

The people that belong to the b) group are supports. Supports already have to buy Sightstone, support item, Locket of the Iron Solari and other support items. There is no place/money for it really.

I tend to get it on Sejuani as it gives everything she wants: Cooldown Reduction, Health, Armour. The passive is really good at escaping pursuers and chasing after low health enemies to lock down with Q and E. The active is good as it allows your team to dive on enemies under their towers or to take out a tower with your team when you have no minions.

Unless you are going for a dive comp or siege comp ohmwrecker isn't the best idea as it isnt super cost efficient and other items can outclass it. I would recommend getting the Zz'Rot portal if you are looking to go for a siege comp.

Depends on how much value you place in the utility. Like Janitsu mentioned before, Ohmwrecker is vastly outclassed by items like Randuin's Omen, which provides 20 more armor and 200 more health for a mere 250 gold and 10 cooldown reduction difference. Unless the Ohmwrecker active can be considered worth more than Randuin's Omen's active (which it honestly isn't), most people won't buy it.

If we look at Kindlegem, we can see that 850 gold is worth approx 200hp and 10 cooldown reduction. This is easily outclassed by the 250 gold, 20 armor, 200 health, -10 cooldown reduction.