The interest represents the time value of money, which may be different to each side.
Maybe the other side thinks that the 7% inflation is just a short spike over the duration of the mortgage.
Maybe they would like to get USD in the future from a stream of USD denominated mortgage payments if they think the dollar is going up relative to their own currency.
Aside from the time value there may be other reasons, too:
Maybe there are regulatory reasons forcing them to buy a certain amount of mortgages or bonds to diversify across asset classes with different risks.
Or maybe it is just their own diversification strategy to do so.
Financial risk relates to how much the value of an asset changes over time (its variance) so in many cases holding “too many” high-growth stocks in a portfolio is beyond the risk appetite for many investors. Lower yield more stable assets are desirable to balance this.