Actually, I see the opposite of what you said.
It's possible you see it this way because you've grown into your position before there was a cloud, or perhaps you had more free money to spend on things (pocket money or so on).
When I was younger, I was poor. The kind of poor I was (not starving, but no disposable income of any kind and certainly no personal money) is enough to kill the premise of learning a cloud provider dead.
What I mean is: if you need a credit card, it's probably not going to work. There's no way I could attach a credit card to something, there's no way I could spend $5/mo on learning, I didn't have $5 to my name, much less a credit card. And the risk of overspending even if you do have some spare income is fucking -scary- as a person who is poor. The idea that I could not have money for food because I forgot to delete something is stifling.
I learned nearly everything I know on 10 year old hardware that I picked up for free or near free. That is accessibility.
As it stands today I'm pretty flush with cash, but I -still- worry about unexpected cloud costs. Mostly because I work with it every day and know concretely how easy it is for the costs to balloon.
So, no, I think it's the same level of accessibility as mainframes, you can't work against an "old" cloud provider that you picked up for almost nothing. You have to put your money where your mouth is, and experimentation has a financial cost.
Only people who can help you foot the bill (university, employer) or who can clean down environments properly (tutorial labs) are going to make it even remotely more accessible, but it still wont be as accessible even then.
Accessibility of running things at home is why many of us are able to do this job, I think the majority of people my age spun up a PHP/MYSQL pairing and started messing with things, it was easy, and it was "free" if you already had a PC, and it could be exposed to the internet.. you learned a lot, incrementally.
This is the fundamental reason why certain tech prevails for so long.