> Why waste 10x more memory?

That sort of question is totally missing the point of why people use these languages, yeah? Languages in the web world don't tend to be chosen based on memory requirements (or speed as this suggests). Are there cases where you want to think about that? Sure.

People have plenty of reasons they'd want to use Python over Go, and vice versa.

The waste in memory is just an additional negative point.

"and vice versa" < Sorry, but no. There's no equivalency here.

The only reason I would ever use python is for small scripts that I only run on my machine and don't need to deploy anywhere.

Maybe 10 years ago Python was an attractive language because Java sucked and C# only runs on windows and there weren't many other good choices.

Now there are many expressive languages that are also statically typed and fast. D, Swift, Kotlin, etc.

The ecosystem is a much bigger deal. There's an officially supported python library for every SaaS product on the market, and many libraries that are best-in-class in areas like data science. It takes minutes to write to pdfs, make graphical charts, edit images, and a million other nuancy, minor parts of apps that you want, but don't want to spend a ton of time writing.

Java is the only static language that features roughly equivalent levels of support ecosystem wide.

Forking 10 processes does not use 10x the memory of a single process starting 10 threads. It's actually almost identical. Both are implemented by the kernel using clone(). Many older tools written in "fast" languages like PostgreSQL and Apache also use forking.

We're not talking about forking here. Python/Ruby apps are actually spawned as several separate processes.

Not for almost a decade. Ruby web servers and job processing frameworks have used forking out of the box since the release of Phusion Passanger 2 in 2008 and Resque in 2009.