Re-startitis is a great name for it. I have it for sure, and always have. I don't know how many times I'd restart in all my previous sim games. Now with S4... oh, yeah I've still got it. I think the main reason I will restart because I'm bored and want to do something different, using a fresh new game. I'm fighting the urge to start one and fill it with Tiny Houses. But I know that won't work because my sims always need more stuff. :D Still, it is tempting...
Once I decided I've deleted too many lots and decided I wanted the old houses back - since I'd deleted lots in several different worlds it was easier to just start a new save. I deleted a save because I forgot to disable the Eco Lifestyle stuff - I'd only played that one for an hour or so, so I had to start again. I started a new save especially for Cottage Living intending to put cottages and farms everywhere - that save has fizzled lately. I've got another couple of saves that I haven't touched in a while...they may be going away, unless I can find a valid reason to keep them. It seems that every time I decide I have too many save games and delete several, I suddenly have a valid reason to start a new one. I apparently am constitutionally unable to have just one (or two LOL) saves.