It’s about optionality. If I either want or need to change jobs. I would much rather call recruiters and say I know the latest .Net Core/EF Core/ASP.Net Core than saying my only experience is with .Net Framework (which is in permanent maintenance mode) and I can deploy to IIS on Windows (even Azure hosts more Linux VMs than Windows VMs).

Especially seeing that when working as a Corp Dev, salary compression and inversion are real and the best way to keep your salary at market value is by job hopping.