Because I'd rather compress ram when running low on memory rather than swapping to my disks. zram is also default on some distros (e.g. Fedora).

Did you read the link? Additional disk swap is optional, and if for some reason you would still like to have one, it's easy to disable writeback, using just the RAM.

And even if one enables zswap and configures nothing else, compressing RAM and only swapping out to disk under extreme pressure is still the default behavior.