I disagree with that, to be honest.
At a first glance, you might think "but where is the shiny carrot that makes me upgrade?" But the thing is - we have dealt with major upgrades at work which broke many things, added many features, changed things in undocumented ways, turned the whole dependency inside out.
That's a horrible experience. You end up running after ghosts: Is it the breaking change, is it a change due to a feature, what is even going on!
Looking at it, Flask 3 seems to be a simple batch of several breaking changes on the roadmap for quite some time. This is good - they thought about batching these breaking changes together to have one big bad one, opposed to like 6 of them over the 2 years. And you can upgrade, and you can clearly see if one of the breaking changes causes harm to your application, without having to worry about hundreds of other changes within the same major release.
