Yep, that is very much intentional! It is intended to be more of a sink for unused resources with minor long-term benefits, in particular for large maps, where apart from your cap-only units, your recruitment completely shifts towards the frontline forts, so all the resources and recruitment points of those deeper inside your territory are basically idle.
Resource selling can be quite good to use for the aforementioned rear-forts, as, unless something goes terribly wrong, they will likely not be using all of those resources anymore, even if they do eventually dwindle down. They sell for a lump-sum of gold, which can let you recruit a handful more dudes per turn. It's randomized, however, so you can't rely on it as the basis for your income.

Public Works is weak and that is good. It is a long term investment. I was expecting a kinda overpowered mechanic. Depending on the size of the province you get 200-700 people (which translates to 2-7 income). Adjacent provinces also get a small amount of people. Can only be build in forts. Minimal Investment costs 100 gold and 500 recruitment points for example. I think it works really well! I wish the population thresholds would be included in the descriptions.
Honestly, I haven't tested selling resources as the premise of permanently reducing resources is a hard turn off to me.

All for more options. Subscribed and updated, I'd like for the devs to implement it in-game, maybe with some other options aswell.

It is to keep the mechanic from being exploitable in the extremes, as the AI is unable to take full advantage of it.

why set population limits though? Why not let big number go up?

Yep, this absolutely makes NO sense at all. I just avoid using public works and population grows nicely. Unsubscribbed. Bye bye.

You have not answered the question

Did you read my post?

Have you checked the description for population limits?

This is deeply bugged. With a positive population growth bonus, I lose about 2K people every turn I use public works. Without public works population increases about 200/turn.