While dice rolls follow predictable distribution, in aggregate, they do not do so in the micro environment. You can end up on droughts on "statistically common" numbers.
We've found this is further compounded by the fact that some resources will naturally end up with poor numbers on them. You might have a game where there's only one good "brick" hex, but two people have commandeered it. That resource becomes so valuable, that you can never acquire it.
While you can technically trade to the bank, the 7 rule means it's hard to acquire enough cards to make the trade.
Sure, if you put your villages on the 2 and 12 you’ll have a really hard time ever getting anything.
If you’re anywhere in the 5-9 range you’ll almost always have something every round.