I think the difference is that if it's a free app[1], the developer wants me to use it and I need to be convinced that it's worth my time.
If it's a paid app, I've already decided that it's worth money. If the app offers enough value for me to pay, then it offers enough value for me to learn what I need to learn.
[1] excluding open source - sure they want me to use it, but that's more like "here it is, use it if you want it". My expectations there are very different, particularly since I can often change things if it doesn't quite do what I want.
If it's a paid app, I've already decided that it's worth money. If the app offers enough value for me to pay, then it offers enough value for me to learn what I need to learn.
[1] excluding open source - sure they want me to use it, but that's more like "here it is, use it if you want it". My expectations there are very different, particularly since I can often change things if it doesn't quite do what I want.