tokisto: That happens all the time here, you´re not alone. It´s that for you, me and about 99% of GOG customers.
I didn't buy anything from the summer sale, because I was playing ADOM and I felt like I'd be playing ADOM for a while still. I didn't buy anything from the Insomnia sale, because I was playing some old PS2 games and it looked like there'll be many to play still. In winter sale I bought one pack because I owned some of that and the games were the sort I really hadn't tried out that much.
I'd like to think that most customers are actually like me and don't feel any need to buy tons of stuff they'll never have a use for.
On average I've bought about 1-2 games a month in here (and really none elsewhere) and usually put in about 20-40 hours a game. But I agree that nowadays abandoning a game is easier because getting a "replacement" is so much cheaper. I think the minority finishes all the games they buy and the minority buys a lot of games they'll never play. Most people probably play their games a good while, but it really takes a certain kind of game to hold your interest over the 30-50 hour mark.