Bash isn’t the only shell. Most systems can use zsh or fish or tcsh or whatever shell you prefer, if you like that better than bash. You’re gonna have to run a shell if you want to use the terminal, though, you understand that?
Defaults matter. There are a lot of situations where you aren't allowed to install whatever you want. It would be less of an issue if other shells or language run-times came preinstalled. The problem isn't really Bash itself. It's the fact that it's often the only dependable option. But thankfully that's starting to change and you can usually find python preinstalled at minimum.