It's because Ubisoft wants you to view their new, "cool" automated sequences. To initiate,
just wait for 2 or more soldiers to attack you at once, then counter. As you've noticed, that's
why there are so many more soldiers in this game compared to previous titles---and many
soldiers attacking you at once.
Ubisoft's soldier AI is still sheepish as fuck even though they tried to tell me different via
Twitter a couple months back. -_- I already knew the outcome of that comment.