If they're not using the bike lane, that's almost certainly because it's unsafe in some way that you're totally overlooking. No cyclist wants to be on the same road as cars.
I have used it myself and it's fine. Better than most roads I used to bike along when I lived in Belgium. Most people do use the bike lane. There is just this one subset, usually in full racing gear, who ride slowly in the middle of the road.
What you call a bike lane I can almost guarantee is made for pedestrians, full of holes, curbs, corners, and also often make you yield to crossing roads which you avoid on the main road.
Few voluntarily bike with cars, especially not those only doing 15 km/h.
See, that I would have understood, but no. It's separate from the one for pedestrians, in very good state, and most cyclists do use it. But there's this strange subset of cyclists who use racing bikes, dress up in full bodysuit, and then ride at a crawl in the middle of the road with other bikes whooshing past on the bike lane.
The main problem seems to be that people (drivers, cyclists, pedestrians, ...) all think they own the road and show very little respect to those around them. Especially those travelling by another type of vehicle. It makes for frustrating and dangerous situations.