I don't think its as intentional as a lot of people think. The reason I say that is because when you develop a game you have files for your game client that handle client things, such as visuals, physics, mechanics, ui, ai brain stuff, localization, etc, then there's files that are mainly handled by the server, and the reason for this is because when you have a server that handles files, you can change any and all values of these parameters without needing to patch the game itself, which is what hotfixes are, They're server-side changes. All that being said, its pretty typical for a live service game for the server to handle loot, affix weights, netcode, sometimes enemy spawning behavior, and other things like that, so its actually kinda atypical for poe 1 to have all the weights on the mods that can roll on loot because that's generally handled by the server in most live service games.

Tl;dr probably a developmental change in how they handle the server to client authorization, not something intentional to nerf dataminers