That's fair then: you're not holding disabled people to a higher standard than everyone else. It's also possible that we have differing ideas of what "grateful" means in this context.
I'll try to explain:
I'm glad that the train driver is driving the train because I could not travel otherwise. But I'm not not feeling pressured to feel like I'm a burden on the train driver.
Going back to when I was a child, pre-autism-diagnosis, pre-mental-health-crisis, I went on a boat trip with my dad. There was a lady in one of those motorised wheelchairs and she was boarded first, assisted by the crew. She apologised to the rest of the queue as she went past for making us wait to board. I remember thinking back then "Why is she apologising? She never asked to be disabled and if she goes on first she can't get forgotten about and left behind. It doesn't hurt us to wait."
This is what I mean by disabled people being expected to be "grateful": the apologising for exercising our rights, the effusive thanks to people delivering our rights as part of their jobs, the pressure to conform to what our parents want us to be as the price for their continued support when they chose to bring us into the world₹, and in many cases apologising for even existing, such as by taking up the wheelchair space on the bus. A lot of people expect this fawning gratitude from us and they have some nasty names for us when we don't deliver it.
So when someone suggests that I or anyone else disabled might try being a little more grateful, well, that really pushes my buttons.
₹ Which is one of the reasons why I think that parents shouldn't be expected to be responsible for their adult disabled children, to take away that element of coercion.