I don't want to re-explain the entire situation, but I do want to point out a major motivation for this was that SDK v1 addons were routinely responsible for ruining people's projects, risking wasting the work of thousands of customer's projects that in some cases they had worked for years on. We provided well over a year for addon developers to update their addons, including providing documentation covering the porting process, and making a range of changes and updates to SDK v2, including implementing a range of feature requests. We also created the LTS release channel in part to help with this process: you can still use SDK v1 addons in the r449.x LTS releases which are officially supported up until the end of next year.
This is not a decision we took lightly but it is essential for the future reliability of Construct and for customers to be able to trust the addons they install, and I'd say that we've actually done a lot of work to try to ease the transition.