Performance and OS integration, that’s what you get with WSL.
Running a full Linux VM on Windows uses up loads of memory, is very slow, requires a load of configuration, and takes ages to boot.
WSL on the other hand is extremely fast, it boots instantly, it’s fully integrated with Windows so it can access the file system and other low level OS functions, and Linux processes appear in the task manager etc. The downside has been some features are limited, as it doesn’t have the full kernel, and file system access is very slow.
WSL 2.0 appears to give us all the good stuff we were already getting, except now with the full kernel and fast file system access. So for a Windows developer who is more comfortable at the bash terminal, it’s a big quality of life feature. Also the fact it now ships with Windows, and is not a feature you have to turn on, shows there’s a big commitment to its future.