Why are sieges so rare in call of war?

Siege battles are very rare in the call of ar gameplay, althought, i guess, there is everything given to it. And i think the players needs to and wants to experience sieges.

If you think the same please share, how would you imagine siege battles in call of war?

I thought the construction of fortofications could be cheaper and/or faster to bulidt.

Also i thought to a new ability, which is to assign units as garrison to certain cityes, or provinces. Units in garrissoned cannot moove out from the province (mooving into, and out to garrison would cost time, like the disembarkation with naval convoys) but get some defence bonus.

Also if you assign garrison to your cityes, the sneaky attacks, or breakthroughts could be least effective throught the gameplay, and makes capturing cityes harder.