Part of the personality of creative folks I'm afraid...I"ve seen so many unfishined projects--devs get excited with a new idea, do a proof of concept, prove to themselves it'll work (or run into a roadblock that they'll "get to later") and then...the next cool idea comes along.
Not sure what it is, but it seems very common - and often a characteristic of many of the most creative devs. It's like they need a partner (or partners) to actually polish and finish their work when they move on to the next thing.
One more indication that code is much more of an "art" than folks realize...