Apparently, Prism Launcher chose to adhere to the idiotic principle of the hidden "trashbin", .Trash-$(uid), invented by Ubuntu. Even though it's based on QT. This can't be disabled. It accumulated 139 GB of literal Trash, fully replaceable, over time. Just ... why? There's even an open issue about this, for over a year, referenced multiple times. I guess I have another point on my agenda.
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
But why wouldn't they use .local/share/Trash instead? Isn't that supposed to be a unified directory for that very purpose?
Because that would take a long time if you deleted a large file in another partition or drive. You could also end up not having enough space to move the file to trash and if the trash directory is on an SSD, it would add a lot of unnecessary wear to it.
To explain it a bit further: when you move a file/directory on the same mount point, moving the file/directory is essentially just a rename operation, which doesn't involve copying the data itself and is a very cheap operation. If you move a file/directory across mount points, you need to (recursively) copy the file/directory, copy file metadata and (recursively) delete the old file/directory, which is slow and error-prone.