I know what you mean, funny thing is that adding a new game to the list feels like would fix the bottleneck
The solution I found is making a list of all my games, sort them out by progress or last time played and then choose 4 games out of that list and play the campaing or reach 100% (depends entirely on your personal objectives) then I log every session in a calendar marking start and finish of said games
Sounds strict but trust me, I've never felt so confident tackling my backlog
Also I recommend wrinting a review about the games, for some reason this keep your attention in the game and makes you enjoy it even more
I've been doing something like this, but more laid back.
I put a soft requirement for myself to beat two games a month.
I should make a more detailed list. I normally pick at random, and so far, it's been mainly helping me play the short games I would never get around to playing since they are short.
So far, I've beaten 10 games this year. I haven't beaten a Game, let alone two, yet this month.