Atlanta may be planning for a big trade return
One explanation for making all of this roster space is that the Braves recognize that they need an influx of new blood on the 40 man roster and they aren't wrong about that. The 40 man had a lot of guys like Shewmake, Shuster, and Tromp that weren't in their long term plans and another group of guys like Allard, Chirinos, and Tonkin who were on the fringes to begin with. Michael Soroka is in his own tragic group given his injuries and lack of minor league options, but you get the idea.
With the Braves big league roster in mostly a good spot, Atlanta may have just decided that the depth they had on 40 man roster was just not sufficient going into 2024. While their measures to change that may look extreme because, well, they are, the vast majority of the guys that were culled weren't likely to move the needle much anyways.
However, another explanation for all of the moves is that the Braves are planning for a big influx of players beyond promotions from the minors or minor free agent signings. That means a big trade or trades could be in the works and that would really spice up the offseason.
The obvious name is Vaughn Grissom who the Braves have been selling pretty hard as an option for them in left field in 2024 despite the fact that he has never played the position in a game before. Were Grissom to be traded to a team that needs a middle infielder, he could feasibly fetch a multi-player return that would require some roster room. However, the more apocalyptic option would be trading Max Fried who is entering his final year under contract with the Braves. Trading Fried seems unlikely given the state of the Braves' rotation and Atlanta's competitive window, but he would absolutely command a large package on the trade market and moving him isn't THAT crazy if the Braves don't feel like they can sign him to an extension.