If people just followed the XDG Base Directory Specification, config file littering would be a non-issue. More and more projects adopt it, even holdouts like Firefox.
I almost want to set up a VM that sets up XDG_CONFIG_HOME as ~/.foobar and see how many apps actually respect it, and how many still write to ~/.config.
And if you install more than one version of go, they get placed in $HOME/sdk [0]. Last I checked, this path is hard-coded with no override, despite this being a known issue for 8 years.
/tmp must be world-writable and for multi-user or multi-tenant systems it becomes a security hole. Storing temporary files in the current user's home directory (or a subdirectory thereof) makes sense.
What doesn't make sense is this blog post about TMP and TEMP, and ending with "I don't know why" (in different words).
The reason is simple: different programmers thought the other name was bad. They were under no obligation to come to a consensus.
Don't forget about TEMPDIR and TMPDIR! Also Windows has its own environment variables for this. But generally, Linux software ported to Windows still use TMP or TEMP.
It makes sense when it's a user option. If /tmp isn't an option due to security concerns, then use $CWD by default. I can always alter the config to some other location if I do not like it. With the amount of programs that litter $HOME, especially with caches, you have to whitelist directories when backing it up. With a naive rsync, you'll find half your transfer is junk.
I don't disagree that it would be cleaner if things were more organized, but I definitely prefer something more like that the person you replied to said, ie "~/.xdg/foo/{config,share,state,cache}"
The only XDG folders that seem reasonable to me are .local/share/fonts and .local/share/applications, and I think both of those are still just conventions, not actually described in any spec.