.NET Core is available on all Linux distributoins, yes. But that doesn’t mean it can be used on shared hosting.
On shared hosting, the hosting provider is responsible for providing the web runtime. For PHP, a hosting provider can use Apache (free and premium). For Python, Ruby and Node.js, a hosting provider can use Passenger (premium only). But no efficient platforms exist to run .NET applications in a shared environment. Which is why, except for a few niche Windows hosting providers, no hosting provider offers support for .NET.