Quote Originally Posted by Dutch_guy
Probably because they are frontier provinces, and can be taken by an enemy bordering the said province. Why waste money and time on a disaster waiting to happen ?

That's my view on the matter.

hmm. i always build those upgrades on my border cities so i can create high quality armies on my borders. retrain high quality troops when they fought off an attack. the troops hold the borders and only a army that massively outnumbers me can drive me away from my borders. and with the citadels and fortresses i can sustain a siege longer. long enough to make a succesfull counter attack.

that is my point of view.