To be fair, you paid once 7 years ago but the developer didn't stop working on the app and didn't make you pay for the upgrades they implemented if anything they have discovered the original price was too low for long term use.
I paid a similar price to that over a decade ago and don't consider this price to be totally unreasonable given they are full time on this now and will need to keep updating the app as lemmy gets updated.
We also have so many alternatives that it isn't an issue if people want to use something that is free. We are in the wild west of lemmy apps due to the Reddit fallout, things will quieten down eventually and a preferred few apps will come out on top.
I got https://www.geocities.ws/misterralls/index.html and now I want to know how Mike Ralls is doing since the enshitification and whether he continued rock climbing