Presumably this 'lack of focus' isn't a problem in your day job.
First of all cut yourself some slack here - it's your spare time, and you hard enough already. You don't need to do more than you are doing, and honestly if you ever don't want to be coding in your evenings you aren't less of a developer or human being if you go and write a book or take a karate class instead.
That said, it's very easy to flit from starting learning one thing to starting learning the next, and it is fun to stay in one place long enough to be able to enjoy some flow in your evening coding.
I recommend that you hook up with someone who needs stuff and go make stuff for them. This can actually be very challenging because maybe what we do day to day as developers at a company is a different skill set to what that person needs. It gives you the chance to try stuff though.
Maybe a local charity needs a nice salesforce setup and some coaching on how to use it and fit its workflow. Maybe some scientists need an app for data collection. Or your local Forrest rangers could do with some custom maps. Once you're committed you're committed, and you'll learn something new for sure.