Matz often cited the "carrot" of much better performance on 1.9 as a reason for the successful transition.

Python3 didn't offer much over python2, so people just saw the downsides, while ruby pushed people to upgrade with the promise that their efforts would gain them better performance and/or save money.

I expect most ruby projects only have rails as its core dependency with all other gems being small utility libraries that can be easily updated and replaced. Python gets used for such a wide variety of things.