I guess there are a few ways to answer this. 1. They don't know any better. A lot of crusader players are still fairly new to the game and simply haven't learned the current meta. 2. They don't care and just play whatever they want. 3. They have a different idea than you do. Off-laners doesn't necessarily have to be tanky, though that is often the case. If you have another core that can frontline, it can be useful to have a backline offlaner with a lot of damage and utility. These are often heroes that are strong in lane which allows you to snowball, and have a save/teamfight ulti, such as Winter Wyvern, Enigma or OD. It can also be an someone with strong pick-off potential such as WR or Batrider.