I will post for my kids who suffer under the same restriction, that it's yet another email address they don't/won't use, but the admin types will only use it for CYA purposes. So risk adverse administrator sends email to the unused address that its "dress like a hippie day" on thursday and 99% of the students don't check an unused addrs so they never know.
"Obviously" they just need an email forward feature, but of course that would require admin effort for the kids that screw it up or intentionally create mail loops or mess with another kids account, so for CYA reasons that can't be done.
So the net effect is we've gone from a modest amount of paper correspondence to no correspondence at all because the tech doesn't work and nobody is interested enough in the message to fix it.
Another problem is for privacy reasons each kids email looks like "a java GUID"@something.k12.edu and nobody wants to use an address or username like that. ts impossible to remember their email addrs or passwords (they're written down on stickers on their devices) but I think it would be funny if its not "a java GUID" but actually their SS numbers run thru md5 or something even dumber from a security perspective.
As an adult, I have an email address like that from my cable company. I don't even know what my cable company email addrs is, much less its password. I've never used it and never will. God only knows how much marketing spam the cable co has sent to it. Maybe electronic bills too, who knows.
If the student account does support forwarding, would that put to rest all of your concerns?
I think it's a false comparison to say it's like your cable address; a school has a multitude of good reasons for wanting to send email to its students. A cable company has mostly terrible reasons.
It costs more and introduces additional complexity. It would be far useful to allow any arbitrary Google Account to join any arbitrary classroom, and trust that Teachers can do a decent job figuring out who is in their classes.
Students have their own gmail accounts vs having accounts issued by the school, who is then responsible for them in some capacity. There is also a cost per-account in Google Apps for Education.
But a system where students brought their own outside accounts would have all sorts of other complexities; in fact, I think they would add up to a greater overall workload. Similarly, the alternative would come with its own set of costs, and the fact that schools are expected to sign up for this service, and that they're generally not run by stupid people, would suggest to me that the overall total cost of ownership, including the fees Google charges, would be less than doing it the other way.
My problem is every sem we need to enroll students with the institution email address. In my part of the world (India), this is not something as easy as it may seem. Google apps is controlled by the Admin and the Google classroom is controlled by the teacher. Only very few use Google classroom and Admin is really annoyed by maintaining student email address.