All of the things you mentioned are designed and tested incrementally. Furthermore software has been used on Mars missions in the past, and that software was also developed incrementally. It’s proposed as the best way because it’s a way that has a track record
TLDR: Google Workspace for Education rug pulled schools on their "unlimited" plans, and the deadline is coming up to avoid paying extra fees. This was communicated in advance, but maybe still a bit quick for a large institution