Oddly enough, it's not wrong in Ultimate Campaign. Sean K Reynolds has responded and pointed out that one of the problems with the kingdom rules in Kingmaker was that settlement magic items allowed for runaway economies, and this was one of the major problems with those rules. To counteract this, two things were done:
1) It is not possible to "sell" settlement magic items for BP.
2) The value of magic items rolled for the settlement are capped at the settlement's base value.
There are a number of people (myself included) who feel that doing both of those things is too much. One or the other would have done the job (and the first one really kicks it to the curb).
It is a completely reasonable house rule to allow the rolled items to exceed the settlement's base value (I do it that way and haven't noticed any problems so far), but it is definitely a house rule. The Ultimate Campaign rules override the CRB if they're in use (and don't forget that a large number of the items rolled will be potions or scrolls,which tend to be vastly under the base value), so don't be afraid to revert to the CRB method, but the wording in Ultimate Campaign was absolutely intentional.
In other words, major magic items slots might as well not exist since most major magic items are over the price range of even Metropolises?