Indeed; it's appalling. This thread [1] shows the absurdity of the situation; almost 8 years, and no signs of a XDG-compatible behavior. At least now you can hide it under ˜/.snap using the experimental flag "system experimental.hidden-snap-folder=true"
[1] Please move the "$HOME/snap" directory to a less obtrusive location https://bugs.launchpad.net/ubuntu/+source/snapd/+bug/1575053