Maybe you just fancy a change? RPG's are quite demanding in the sense that they require a fair bit of investment. Not just in time (which can be over a hundred hours in some games), but story too, as the best of games lead to you coming to love your character and genuinely enjoying the decisions he/she makes that impact their world.
Being human, we like change, experiencing new things. Some more than others - for some people, they will quite happily stick to one thing for huge amounts of time until its absolute completion. For others, they are like butterflies, as they feel restricted when tied down to one thing, preferring to flutter about freely from 'thing' to 'thing'. And there are those of us somewhere in between too, of course.
For me, I will generally play a game for a few days to a couple of weeks, or perhaps months in some cases, before putting it down for a while. For example, I may play on the Minecraft server for a couple of weeks while I'm in the mood, and then just leave it for a few months. Or, in long RPGs like Mass Effect, I'll play it for a few days/a week and then put it down for a month. Our bodies can go through phases, or rather just searching for variety in our lives.
Don't put yourself down for this. If you don't finish a game, it may just be that you're looking for something else as a change. Go with the flow, and if you really want to finish a game then come back to it later.