It changed during the pre-1.0 era when the team were very clear about the potential for changes. The big changes were made with plenty of notice and short term backwards compatibility baked in. MVC 5 is still there and still being supported - deliberately choosing to use Core should have been a calculated decision based on what you needed and appetite for risk. If there's a bad influence from the world of JS it seems much more around devs deciding to go into production with "the new hotness".

Moving to npm/bower for front end stuff makes perfect sense, NuGet is a horrible way to deliver client side code, wasn't supported by the majority of library producers and was unknown by anyone who didn't have a .Net background.