If I see an application that is $50, I can quickly quantify that into hours I need to work for this to be paid off. I can compare the value I am getting to the amount of currency that I expend on it. I know that if I need to in the future, it will always be there for me to rely on.
If I see a service that is $12 a month it becomes a much harder game. Sure it might be worth it for the first month, but the second one becomes a much harder decision. Do I unsubscribe, and lose all the data that I have stores, or do I pay another $12 and hope that it continues to be useful to me in the future? In the future I might need to sign up again, which is a lot more hassle than it is worth.
All of these "small" subscriptions are beginning to cost me more than I'd like.