Lemmy is restricted too without login (as well as literally everything)

You mean that you cannot comment or vote without an account? That just makes sense, because you need an account to tell the server to save some data of yours. That has to be connected to an account. Search does not (unless you are fixated on saving all actions of the user on the platform for behavioral analysis)

The funny thing is that the last person I saw make a huge deal of this on Lemmy/Reddit, didn't have a huge number of github commits over the years (they definitely had some, so they were active though, but even our newbies at work overtook them in months)

Maybe you didn't know, but not everyone in IT (job or hobby) writes code.

Creating a login is free too

Not really: you have to give personal information.
It's not much of a problem until they only need an email address and are not too opinionated on your provider, but it's not rare at all that platforms also require a phone number (either upfront at registration, or discord-microsoft-style, locking you out of your account untill you give it them) which for the most part won't be private at all. Thus, you are paying with your data. For something (repo content) that the maintainers wanted to be public and free.

Creating a login is free too, and so is downloading source code

What about the Wiki and Discussions? Several others said things that make me think it's under A/B testing.