Have written a lot of code over ~35 years. Not a fan of trailing commas in any language I've used.
Now extrapolate to the whole industry. There's a cost, regardless of how someone might want to value it.
What a joke.
I mean sure, if people spend most of their day just mindlessly copy pasting crap then perhaps I guess. But compared to the amount of time I find I spend thinking about the actual problem at hand, the single keystroke to edit a comma is a rounding error.