the main reason to stay with 4.8 is compatibility with existing code. for example webforms, is only supported by .net 4.8. Its main downside is lack of new features. Only security updates (which are allowed to break existing features if required).
.net offers improved performance, new features, cross platform support. hosting on linux, even in azure, is cheaper than windows. Its main downsides are cost of porting old code and the requirement to stay current with Visual Studio and runtime. (LTS version are only supported for 3 years).