Discourse is free, servers, domains, and our time is not.
This has nothing to do with corporate environments, it’s just common sense when there are so many variables at play. Lots of work is done to make upgrades seamless and if you would prefer to give your time for free to resolve significant blips that’s your call - but personally I prefer to know that the nonprofit and volunteer communities I host are going to be down once for a painless upgrade, as opposed to a protracted period.
The smallest VPS at DO will suffice to de-risk upgrades as long as the test is representative - if you’re a decent SA then that $5 is a the cost of a cup of coffee, and fraction of your hourly market rate.