Are you getting an error message when running the install?
I was having the same issue, and it turned out to be an invalid NuGet package source. The installer fails to get the latest templates if it cannot access any of your package sources.
When I ran PS C:\Users\me> dotnet new --install Microsoft.AspNetCore.SpaTemplates::*
I would see an error in the terminal
Restoring packages for C:\Users\wacht\.templateengine\dotnetcli\v2.1.4\scratch\restore.csproj...
C:\Program Files\dotnet\sdk\2.1.4\NuGet.targets(103,5): error : The local source '\\privateserver\NuGet' doesn't exist. [C:\Users\wacht\.templateengine\dotnetcli\v2.1.4\scratch\restore.csproj]
After I removed the inaccessible package source, the installed updated my local SPA templates and installed the Vue template.