I don’t think dropping legacy support is due to boredom. It what allows them to keep moving forward without being saddled by every decision from the past.

How long should they have kept PPC or Classic support?

Microsoft is in a funny position. Backward compatibility is seen as a competitive advantage, especially in the enterprise market. However, it’s that very compatibility that makes people avoid adopting new technologies, because why bother? We see Microsoft throw so many things against the wall, and almost nothing sticks. Meanwhile, Apple tells devs to jump and they ask how high. Devs know Apple is going to cut support, so its update your apps or be left behind.

To really make a change, a person needs to be all-in. Dual booting Windows and Linux/macOS, for example. This is a sign a person isn’t all-in and they don’t really make the change, or it takes significantly longer. When a person goes all-in and burns the boats, they are forced to find new solutions and make the changes needed to make the new thing actually work.