[jonnytran]

This tells me that you've never used a well-managed language or framework. Those aren't the only two options.

Ruby 1.9 was released around the same time as Python 3, with a similar amount of large breaking changes, and no one was holding on to Ruby 1.8 the way the Python community held on to Python 2.7. You could keep using it if you wanted to, but no one did. Ember.js is another example that I've used that was refreshingly well-managed, with a clear (oftentimes automated) upgrade path between minor releases. Using semver and LTS versions, it didn't just break backward compatibility without a significant deprecation period. Those are just a few examples off the top of my head, but I'm sure other good examples exist.

When things are well-managed, you as a developer have the freedom to upgrade when it's a good time for you. When you have production software with real users or a business that depends on it, you can't always just drop whatever you're doing to upgrade, which is why backward compatibility is needed.

If it's done right, there's a self-imposed drive to want to move to the latest with all its improvements. On the other hand, with Python 3, they took away things that people cared about, leaving developers not only with no drive to upgrade, but an irrational impetus to hold on to what they had, even when the situation was fixed at a technical level.