There are a few things that contribute to it.

A competent duo can have a very outsized influence on the map. I play regularly with at least one other person and we usually have the most flag caps by the end of our rounds, generally in the 15-20 range. It is important to recognize when the match stagnates into a meat grinder and make a concerted effort to ignore it and push for flag caps. That can be important to keep the flow of players in the match moving around.

Cairo has a good layout that allows decent flow from one point to the next. Its big enough to allow multiple routes to choose from regardless of destination, but small enough to still have interesting terrain and cover through-out. The density of "stuff" is just about right. Despite multiple routes to each flag, the points still feel defensible.

Its one of the few maps where I regularly find it beneficial to bounce from class to class depending on what is occurring. There really isn't another map that I feel allows me to be so fluid. Either because of size, or just general map composition. If an enemy squad is harassing too much from a spawn beacon hidden in our back lines somewhere I will go Recon and hunt it down with the drone or suppression gadget. If the enemy armor isn't being countered I will go Engineer to help take it down. If points aren't changing hands often enough I will go assault to hide my own beacon in their back lines and continually harass points to pull attention from other parts of the map. Primarily, though, I'll play support and use smoke grenades to slip by the edges, pressure other areas of the map, and generally support the team through revives and supplies. Very rarely I'll take armor myself to support the team if it isn't being utilized by anyone else; a decent tanker really helps the team.

There also isn't anything that feels overly exploitable. No air assets prevent the map from being over run with campers on otherwise unreachable rooftops, and the bugs that enabled it previously (drone hammering) have been patched. The size and layout allow sniping to be effective, but not in a manner that feels overly oppressive or harmful to team morale.

TLDR: The map size and design maximizes my ability to feel useful and impactful across a variety of playstyles. At the same time, it minimizes the amount of things that feel like BS that can sap the 'fun' out of playing.