I think it is equally due to the high level of individual unit movement points and significantly less ZOC-lock than other titles. That is, while orders do limit the number of units one can move, each unit can be moved multiple times and each move frequently results in multiple tile moves, on top of that forced march can push units even further.
The effect is an initially surprising degree of movement and fluidity for an (initially) small number of units. In the early and midgame, due to fewer units, map openness, the degree of movement freedom, and the sheer number of moves one gets to take in IGYG fashion, while their opponents units sit frozen, unable to reaction; it is almost impossible to create fronts and solid lines of engagement.
Units quickly rush across empires (especially along controlled coasts), and dance ‘through’ and around enemy positions.
Further thought: the attacker advantage works in concert with the above to make early and mid games warfare feel like COPA-style futbol in comparison to the more static UEFA-style football of previous titles.