In an open room where half a dozen or so people sit, if two people stand up, walk into a conference room, and shut the door, that's weird and curious.
This also happens all the time, thus not weird. (or people don't talk ...)
Personally, I've been very happy with the environment. It helps that the open part of the office is bright, quiet and pretty sparsely populate.
Why don't you introduce the rule that entering another office is only allowed for scheduled appointments and emergency cases (life is in danger or the production server crashed).
There were things I liked at that company (mostly the people), but everything about the way the offices were set up had me on edge all the time. No private meeting space, not a single person had their back to a wall, people were thrown into offices at random with no regard to who was on what team...
After I got laid off, I landed at a place where I work in a cube farm, and it's so much less stressful.
I hope your leaving was voluntary, though... if it was, then congrats on the new job!
(and, yeah, I figured out who you are from the about section on your profile... I used to sit right behind you)
Yes, people do use it for those conversations, but you have to walk past all the business/marketing/sales people and your boss(s). Outside the office is a place to confide - where an "official" meeting or neutral meeting room is a place that puts everyone on the defensive, more so than anywhere else.
The idea put forth by Mark Cuban that "there should be no secrets at a startup" is extremely unfounded in my opinion - unpopular opinions or contrary positions frequently only flow in privacy as to not cause embarrassment or hostility.
That's a barrier compared to just chatting at someone's desk. Or the developer doesn't want to move their laptop, so they'd rather stay at their desk that go to the meeting room.
That leads to too many conversations in the open plan office.