I didn't have much time for a proper response, so I fed my quick thoughts into ChatGPT and ask it to make that into a full answer.
You might need to clarify whether you're asking about general player preferences in RTS games or specifically about their behavior in the current alpha of 0 A.D.
If it's the latter, I have some insights:
APM and Gameplay Style: Fast economic growth (booming) requires high APM (actions per minute). Many players, especially those who aren't pros, find it easier to focus on either growing their economy or fighting, but not both simultaneously. As a result, they often switch from economic growth to combat at a certain point. Engaging all units in battle means there's less economic management needed.
Full Population Strategy: Reaching full population with all upgrades provides players with confidence. They know their opponent won't have more units or better technology if they themselves have maxed out their capabilities.
Early Attacks: If an opponent attacks early, they spend significant time moving their units across the map, which can be inefficient. Subsequent reinforcements also take longer to arrive, potentially weakening the attack.
The question might not be about wanting smaller fights. Instead, your concerns could be addressed by improving the UI to make unit management easier.