You are completely right OP.
I am embarrassed, even ashamed to be associated, simply by virtue of being a parent and sometime pushchair user, with those self-absorbed, selfish, ignorant parents who think that their wants, their petty, temporary inconveniences, are more important than your lifelong needs. I cringe for them. I feel deep sympathy for you.
Wheelchair spaces on buses only exist because of decades of really hard, frustrating, tenacious campaign work, by people with disabilities and their (few) allies. Campaigning that was necessary because society at large chose to view disabled people as sub-human, not as real people who had worthwhile lives to live.
If pushchair-using parents feel strongly, about those few years of inconvenience in their otherwise objectively easier lives, they can mobilise themselves, do the work and do a bit of campaigning of their own, for pushchair spaces.
Selfish cuckoos that they are.