Exceptions exist, like The Americans, but comedies are usually more guilty for complicating couples’ lives for the sake of the laughs.
As such, the producers apparently thought Ross and Rachel’s status quo was a snoozer.
(You’re the Worst has successfully kept that conceit going for what’ll be four seasons.)
There’s a bit to unpack there, though Kevin S. Bright’s comments to Metro basically say that the Friends team fell into the same trap that many TV staffs get into when romance is on the table.