Quote Originally Posted by Haudegen
Maybe there is an affinity of the theologians guild to certain cities?

Another example might be the swordsmiths guild. I never was offered one. But I finally got the swordsmiths guild HQ when I conquerered Toledo. AFAIK the spanish smiths were quite famous for their skills. Maybe there is another affinity?
If you crack open the game files you will see that Toledo has an increased chance of being offered a swordsmith's guild, so yes. Most guilds have 'favored' cities.