It is the Arch devs who do that. By default you are on the Arch Stable branch, which is similar to Manjaro’s Unstable branch.
The terms Stable and Unstable are somewhat misleading, they have little to do with stability of the system, but more with update frequency. So in that regard, pure Arch (including EndeavourOS) is more bleeding edge than Manjaro, which is slightly delayed.
It’s a double edged sword. On one hand, Manjaro is less prone to breaking, because its updates are curated and tested on other Manjaro systems. On the other hand, Manjaro updates are huge, and whenever you have such a large update, chances of something breaking are higher. I don’t have much experience with breakage on either distro: I’ve used Manjaro for about a year, and never had anything break, and I’ve used EndeavourOS for about three weeks, and also, nothing broke yet, to knock on wood.
But, I did have to be mindful of the last kernel update on one of my computers running EndeavourOS. Had I not installed a backup lts kernel, I would not be able to update to the latest kernel before the drivers in the AUR were updated as well. I foresaw that there could be an issue with it and had asked about it on the forum some three weeks ago, and so I was warned about it in time and ready.
Whenever you’re using a rolling release distro, it’s a good idea to learn about Timeshift. It can make your life much easier in case of an update that breaks things.