Yeah, unless you left your Supports completely unattended and ignored them 100%, it was actually pretty rare to have your backline attacked. The enemy usually will go for a flank attempt if they feel their team is neglecting to watch out for their team mates in the backline, because otherwise it would never work.
With 5v5, everyone usually focuses on what’s in front of them due to having one less team mate. So a confident flanker will take advantage of this and wipe out (or try to) your backline.
Let’s just be honest with ourselves, anyone above Diamond doesn’t even bother because players are typically more aware of their backline. Where even Plats will seemingly mute their Supports who are screaming about a Tracer destroying them and need some help.