I do complete side projects, but I don't complete more than I complete. Often it's because trying to balance multiple projects when each is using multiple frameworks in different ways becomes a massive headache, things get paused and then canned because now there's newer buzz-word frameworks to use!
Side projects are natural places for programmers to get lost in this kind of bike-shedding/yak-shaving/etc., since they're not under the same kind of "this needs to ship on Tuesday or I lose my job" pressure that work projects are.
And in fairness, one of the better reasons to do a side project is to get up to speed on some fashionable technology so you can get a better job; that may well be of more value to you than the nominal deliverable, in which case it could make sense to prioritise it.