It doesn't make the economics any different. In a browser environment, you're maybe looking at the acceptable lease being 100MB for 1 second. Much more than that, and you start hitting limits of what browsers will let you do on low-end phones. Longer than that, and we're back to the user-observable latencies being too long.
100MB for 1 second just is not much of a deterrent.
Sure, but end users as a group still have a significant amount of RAM.
Even on a low-specced machine you can afford to have the currently-active website tab consume a few hundreds of megabytes of RAM. It was mostly sitting idle anyways, so most people aren't even going to notice. Multiply that by a few thousand concurrent visitors and you're burning hundreds of gigabytes without anyone caring.
Some scraper being forced to install hundreds of gigabytes of extra RAM in their crawling node? They will notice having to go from a $0.50 / h instance to a $15.00 / h one, solely for the extra RAM requirement.
100MB for 1 second just is not much of a deterrent.