Our city buses have 4 spaces for buggies or one space for a wheelchair and 2 for buggies, which is usually enough.
In the dark ages I just had a stroller which folded easily or a big pram which meant I had to walk everywhere. I think the new "systems" make life so much easier for parents. Sometimes it's impossible for them to fold them on buses if they are laden with shopping and it seems unreasonable to ask them to manage shopping, baby and toddler and fold a pram. There would be nowhere to put a folded pram anyway, as another contributor pointed out.
The buses are every eight minutes so and I don't think any reasonable person would mind a short wait rather than have a mum and kids thrown off. I've never seen that happen, though, usually there is enough space for everyone who needs it. Even those blasted wheeled tartan shopping carriers.
I saw a nasty row once, before the new buses, where the driver of a very crowded bus told a woman she and her pram, sleeping newborn and 2 other children had to get off for a wheelchair user. She was willing to do so and asked for a refund of the bus fare which was refused. She asked for something to show the driver of the next bus that the fare had been paid and the driver refused that as well. So she said she wasn't getting off then.
A few people joined in on both sides, I could only spectate from the back. The chap in the wheelchair said it was ok another bus would be along soon but the driver was determined the woman (in tears by now because she had no cash) would have to get off. He threatened to call the police and was vile to her. She was sobbing and so were the kids.
Meanwhile another bus arrived, the chap in the wheelchair got on it and off it went. But still the driver wanted the woman and her kids off. A really big chap, a few rows in front of me made his way to the front and explained, loudly, to the driver that he needed to get back in his cab and drive.
It made the papers and the driver was sacked but I've never forgotten how utterly horrible he was.