I've been developing with .NET since 1.1. The initial appeal of ASP.NET WebForms was due to the fact that you could build software similarly to the way you build Windows desktop based apps. State was managed in an unmanaged environment. You didn't have to worry about varying browser capabilities / quirks due to the lack of standardisation at the time.
Fast forward a few years and all of a sudden you have browser standards and amazing MVVM frameworks. Everything you needed ASP.NET for was no longer required.
I still work on enterprise .NET systems and it's no surprise as to why startups look to alternatives. Sure the tooling is amazing but so are many of the other tools out there. After using simple web frameworks like AdonisJS I see no real reason for building your service layer (let alone your app layer) in .NET.
Fast forward a few years and all of a sudden you have browser standards and amazing MVVM frameworks. Everything you needed ASP.NET for was no longer required.
I still work on enterprise .NET systems and it's no surprise as to why startups look to alternatives. Sure the tooling is amazing but so are many of the other tools out there. After using simple web frameworks like AdonisJS I see no real reason for building your service layer (let alone your app layer) in .NET.