In many other milongas people sit where they want and inviting is much more relaxed.
That's a huge factor.
Around here, people show up whenever they want and wade in. Once the chairs fill, people stand, which in most places describes the situation for almost everyone. What few chairs exist are rarely around tables, but at the edges of the dance floor, facing the dancers – and chairs around tables are dragged out to that position. So, you have a standing mob walling in the ronda, some seated people trying to peer around them, and a few tables stuck way back in corners, often stripped of chairs.
This results in most invitations consisting of one person turning to another nearby and asking verbally. A few people push others around and hunt specific partners. Everybody seems to
understand the cabeceo – it works just fine at the start of the evening when the crowd is small, and at the end when it has thinned out (around here, a milonga that runs from 9:00 p.m. to 3 a.m. will be crowded from 10:30 p.m. to 1:30 a.m.). But when you're most likely to have lots of potential partners, it's physically challenging.
As a bonus, our milongas go for subdued lighting. People claim it's to make things more romantic, but the truth is that it hides sins: water damage on the floors, wobbly seats, wilted plants, crud on the exterior of windows nobody can reach to wash, etc. I know this from direct experience trying to clean up a studio.

That makes the cabeceo even tougher.
One organizer periodically held events with three-sided assigned seating: women on one long side, men on the other long side, and couples and groups at tables at the far end and on the little stage. She kept the lights up to facilitate the cabeceo. Standing was prohibited (politely); she sold one ticket per seat and then closed registration.
And . . . nobody much liked it. Talking of environment, it was a bad fit to the
social environment here. My region is one where people like to decide where to go at the last minute (often after going out to eat), pick up a few friends along the way, show up fashionably late, and stand around being kissy, huggy, and chatty. Few people care to suspend those habits for tango.
This is one reason why I keep belaboring the point of regionality. I know that some people here like the
idea of all milongas everywhere being like the mythic archetype of the
época de oro, but that's a terrible fit to many places in the current era, both physically and socially.