Deep Sea, Castle Eggman, Arid Canyon, and Red Volcano were all completely remade because the previous versions lacked quality. The community agreed they needed to be overhauled. In fact, CEZ had already been remade for 2.0, but needed another remake.
Egg Rock was infamous in 2.0 for being a massive difficulty spike. The sections in question were removed to make the level shorter and a little easier. There were also too many gimmicks, and many of them weren’t used well. Egg Rock itself is planned to get a remake for 2.3.