Nah. I disagree.
The convention I have always used, and thought was best was this. The person in front puts their stuff on and puts the divider down. The reason being, it’s much easier for them, as the person behind is often, if not always further away and has to lean over/sometimes just can’t reach. Especially when there aren’t many divider things.
I mean, you can leave a space and grab the thing when ready…but to my mind, it’s not so much the not doing it. It kind of makes me think it’s indicative of general selfishness. ‘I’m OK, everyone else can fuck off’ if that makes sense. It’s literally zero effort to put your own stuff on and put the divider down afterwards, and just makes everything easier, and indicates you might consider others too.
Anyway. I might be overthinking it.