In my experience, running a web application on a VM which can handle 10x the normal load is pretty cheap. And occurences where a traffic spike is more than 10x the normal load are so rare (once every couple of years) that I can deal with it manually.
But understanding of scaling seems stuck in 2012 when these systems were required for even moderate sites, particularly if slow frameworks are being used. The rise of cloud use is definitely part of this mentality. An ingrained believe that horizontal scaling via vendor is the only way.
But meanwhile, in 2023 where we've seen a 500x bump in what servers are capable of and vertical scaling and it's simplicity can just "get you there" for 99% of sites.
The bigger plus is the temp environments, that free up a lot of developer time in my experience; they solve a lot of boring, time-heavy communication problems. A pull request can just spin up a temp environment which a designer can eyeball at the same time as the code is being reviewed. Means less rework.