The bank doesn't care what interest rates are going to be next year, because they sell the mortgage now and collect the cash for it. The buyer cares, but the buyer is probably a hedge, pension, or sovereign wealth fund that in theory at least should be able to estimate & offset interest rate risk.
I wish the article went into more detail about exactly who the losers are in this system. I suspect that it's essentially a policy by the U.S. government to increase social stability (in the form of homeownership, stable residence, investment in communities) at the expense of holders of U.S. dollars and dollar-denominated assets (i.e. most of the rest of the world). In other words, it's transferring wealth from non-citizens in exchange for keeping citizens happy, which is a pretty typical government play. It also looks like the system is on the verge of collapsing, in the sense that it pumps up house prices and encourages artificially low interest rates and high inflation, and hence an increasing number of American renters are being caught on the wrong side of the equation.
Interest rates are set in a competitive market. At any given point, there's a relatively fixed supply of money being put into what's on offer.
For buyers like pensions, it's simple: get the highest rate they can with acceptable risk and diversification. Keep in mind that not all of a fund's assets should be invested in super-long duration loans. Anyone running a fixed income portfolio understands this is a major source of risk (interest rate risk) as long-dated bonds are one of the most rate-sensitive investments possible. You'd do better with a blend of short, medium, and long-duration debt to ensure you don't end up hosed when rates move the wrong way.
Also keep in mind, many net buyers of this stuff are using it to offset long-term liabilities -- insurance loss payments, pensions, etc. Insurance companies will adjust premiums based on earnings of their investment portfolios.
And finally, keep in mind that interest rates aren't just a video game. There are major "real" drivers of them, economic growth being one--the demand for credit and its supply absolutely shifts over time, and throughout the business cycle. Real economic variables like demographics, home building, population shifts, the number of retired (more savings) vs working (more wage income) people in a population, etc. cause this stuff to move around a lot. If someone gets a higher rate, it's because at the time, there was more demand for credit, it wasn't just someone "losing" or getting "ripped off" that made that trade possible.
One thing to note about securitization and prepenalties:
The risk of prepayment being priced in, but there is the opposite balance of the fact Mortgage Originators (not the borrower) in some circumstances do have a prepayment penalty; this period is typically up to 6 months after closing.
So, they care, but the risk is (like so many in finance) heavily abstracted.
People who dont qualify. People who misuse it. As is the case with much debt, there is debt given to people who consume it, spend it, lose it and owe it; and there is debt given to people who invest it, accrue with it, and profit from it. Many people may stumble through the process and benefit from it, while the purchasing power of others who cant get it is diluted.
- fallout risk https://www.investopedia.com/terms/f/fallout-risk.asp
- pipeline risk: https://www.investopedia.com/terms/m/mortgage_pipeline.asp
For the fallout risk an originator can typically model the impact on the value of a mortgage with a conservative low digit basispoint estimate (following past fallout patterns that have been observed for example), for the pipeline risk the originator may do some more exotic price modelling by deriving implied interest rate volatilities from market prices (of interest rate derivatives).
Both risks are relatively speaking minimal given their short horizons and the (current) low volatility of interest rates.
I am impressed with the quality of the website linked to by the author of this thread, great read!
If the consumer doesn't like that they can get a lower cost variable rate mortgage just as easily.
The socialization-of-losses aspect comes through interest rates. When wealth isn't held but is traded on markets, there's an incentive to hold interest rates artificially low, because that makes asset prices artificially high. High asset prices benefits all asset holders, so you can make people happier than they otherwise would be simply by keeping rates low.