The Fairphone 4 at least you could replace the battery without any screws at all. It took seconds and it's been extremely useful for me.

On the Fairphone 2 you could even replace the screen without screws. It made it unstable and prone to getting loose, and it was a huge improvement when the Fairphone 3 started using screws for that. It was a fun gimmick, but for something you replace that rarely, it's really not worth the sacrifice.

Screws keep them repairable and sturdy. It'll no longer be as easy to bring a spare battery to replace on the go, unfortunately, but unfortunately, it's a trade-off, and with most people already not doing that, it makes sense where they ended up.

On the flip side, the battery of my Fairphone 3 had a tendency to disconnect when it was shaken too strongly for its taste, rebooting the phone…

So I'd consider screws to be an improvement actually.

haven't had this problem with fp3+ even when it drops on the floor

If in 2025 your unscrewed battery is disconnecting evening at vigorous shakes it is not your fault at all. So that doesn't explain the "bring in the screws".

There must be something to tighten the contact between the phone and the battery, every other manufacturer uses glue, Fairphone tried to solve this problem with plastic clips before and it wasn't reliable enough, so I'm certainly not gonna blame them for doing it with the most effective method that doesn't compromise repairability.