Since your original question was
Why is nuget.org not listing supported frameworks for a package?
It's apparently considered P3 but it is planned for the major gallery redesign.
Question
Why is nuget.org not listing supported frameworks for a package? Isn't this information important?
To be more specific, I am talking about the package page
https://nuget.org/packages/[PackageName]/
If this would get displayed on the page, I assume the NuGet manager in Visual Studio will be able to display it too. I will be able to know exactly what platforms the package targets
Solution
Since your original question was
Why is nuget.org not listing supported frameworks for a package?
It's apparently considered P3 but it is planned for the major gallery redesign.
OTHER TIPS
I can't tell you why NuGet Gallery doesn't implement this feature. Since it's open source and hosted on GitHub, you are free to implement it yourself and send a pull request to the authors.
For now you can use NuGet Package Explorer to do it manually. Just choose Open a package from online feed option from the main menu and find your package. NPE will download and display its contents for you. You can see which frameworks are supported there.