The single return best practice comes from the old days of C. Back then, compilers didn't inline function calls as aggressively as they do now, and the overhead of a call was a relatively significant fraction of execution time. That led to longer functions being a good idea.

At the same time, C does not have any features for reliably managing resources. No GC. No C++'s RAII. Instead, you have to be careful to release every resource you acquire in the body of a function, along every execution path.

In that world, avoiding multiple returns makes a lot of sense because it ensures every execution path reliably reaches the end of the function so it's easier to ensure resources are released.

We aren't in that world anymore, so the guideline no longer applies. But it wasn't a stupid rule. It's just unhelpful to take it out of its original context and expect it to apply to a new one.

"Check your boots for scorpions before putting them on" isn't a dumb rule in the desert, but it is in Antarctica.