FWIW, xz is also a memory hog with the default settings. I inherited an embedded system that attempts to compress and send some logs, using xz, and if they're big enough, it blows up because of memory exhaustion.
I didn't mean to ask why the defaults are defaults, but rather why anyone would use the defaults rather than settings more appropritate to their use case?
It's not like xz is unable to be lighter on memory, if that's what you want. It's an option setting away.
Then why use the default settings?
I tend to use the maximum settings, which are much more of a memory hog, but I have enough memory where that's not an issue.
Just use the settings that are right for you.