I have no idea if any of this is correct, but my understanding is that mortgage rates are set, more or less, by the market. You have buyers(say, pension funds)

I have no idea if any of this is correct, but my understanding is that mortgage rates are set, more or less, by the market. You have buyers(say, pension funds) with a lot of cash that they need to invest in a relatively safe way. They bid on mortgages and whatever they're willing to pay for those loans sets the mortgage rate. Up until(or maybe still including) now, the Fed has also been one of those buyers in an attempt to push down those mortgage rates. Rates are low because there aren't a lot of alternatives for safely storing cash right now. Normally you could buy government bonds, but rates on those are also negative for the same reasons(demand along with fed buying). When rates on government bonds rise, or when it's obvious we're back in a period of consistent inflation(likely, given the fed's weak move today), investors will have other options and the demand for cheap mortgage debt will dry up at the current price, pushing rates higher.