It looks like this was a larger decision from the lemmy development community in an attempt to eliminate karma farming. They say it’s psychologically damaging, and as someone who looks at them a lot, they may be right.
Here’s a GitHub thread discussing it where our Voyager dev weighs in:
https://github.com/LemmyNet/lemmy/issues/3393#issuecomment-1779400639
GNU AGPL is a standard open source license, even Voyager uses, and has 0 impact on how you consume a lemmy instance’s API. The GNU AGPL main sticking point is just making sure that if you modify the source code, you have to make that modified source code open source.