That was a standard that existed because of older, ‘linear’ SDLCs. It stopped being the case when Agile development took over. When you’re using Waterfall, and all your milestones are planned out before a single line of code is written, you can do that.

Modern software development doesn’t work like that, and it’s silly to use nth-degree nested decimals (0.1.0, 0.1.1.2) when you can just use 1.1, 2.13, etc, and call something RC1.0 and 1.0 on release without bothering with internal version numbers or project codenames (or just keep the working version numbers anyways).