How much money and resources do you think goog is spending on an ongoing basis to ensure they sell fewer Chromebooks to schools (and in general) in the future?
It's much easier (and more profitable / less expensive) from a program management perspective to instead deprecate the bulk of these cheap machines after five years to ensure "consistent user experience".
I hope I'm wrong! My experience with capitalism tells me I'm probably not. Less e-waste isn't profitable in the short to medium term. :(
The hardware manufacturer is a different story. They love nothing better than to collect a laptop price tag on a laptop replacement schedule while only having to deliver a chromebook performance and absolutely zero os/software related customer support or windows license.
Google just makes the chromeOs?
I have a Chromebook that was released in 2019 and will get updates until 2027, so there's definitely not a rule that they can only get updates for 5 years.