Cyclists rarely leave the bike lane for pleasure, it's usually either because a car is parked on the bike lane, pedestrians are walking on it, or because there's litter or a bad surface (bikes are much more sensitive to uneven road surface, but at the same time bike lanes, especially those that are separated from the road, are often built with lower standards than the streets).

Reading your comment one would think cyclists are just suicidal for the fun of it, but try to think of them as humans who have a goal to achieve and are trying to achieve it with the best efficiency/safety balance they can find, like other people. Cars are everywhere on the road, impeding and endangering cyclists, so it's often a matter of trying to find the "least dangerous" way to do something, and that might even involve getting on the wrong side of the road at times. But it's not for fun.