The ecosystem is really it, C# as a language isn't the best, objectively Typescript is a much more developer friendly and globally type safe (at design time) language. It's far more versatile than C# in that regard, to the point where there is almost no comparison.

But holy hell the .Net ecosystem is light-years ahead, it's so incredibly consistent across major versions, is extremely high quality, has consistent and well considered design advancements, and is absolutely bloody fast. Tie that in with first party frameworks that cover most of all major needs, and it all works together so smoothly, at least for web dev.