Obviously it is not wheelchair users that are the problem, it is folk who abuse the system.
It makes sense to allow them time to get on as otherwise they would be holding others up and that would cause complaints as well. It also allows airport staff to be freed up to go and help others.
The plane won't leave without us so what does it matter.
Have to say that children under five and an adult is acceptable but the whole family is a different matter. Only once had to do it with our grandchild and I went on with him as he was sleeping and I was carrying him at the time. The other five adults queued.