It is very common for young people on every generation to be part of the left-wing movements. But I think they are focalizing in a superficial problem, instead to find solutions to more critic challenges. Do non-straight people suffer discrimination, etc?. Yes, but there are other more dramatic problems such as: homelessness, fentanyl epidemics, public health, etc.
Good thing you can have the right economic politics at the same time as being queer. Young people identifying as LGBT does nothing to detract from their other left-wing views.
Common but not universal - as recently as the 80s young people tended to be more conservative than average. The giant age gap we see today with young people way to the left of the rest of society is pretty unusual.