“It’s a bad idea because it’s shared global mutable state that crosses security boundaries.”
The sticky bit was invented in the 1970s to keep programs in memory, then recycled to stop users deleting each other’s files in /tmp. POSIX shipped five ways to make a temporary file, and three of them you must never use. Every one of those patches treats the symptom. Fifty years of workarounds for a directory that should not exist.