Mortgage rates are based on bonds and bonds are often the target of safe haven buying in times of geopolitical distress. The situation in Ukraine certainly qualifies and the bonds have been improving ever since.
For mortgages, it's not quite as simple because mortgage-specific bonds don't tend to benefit as much from safe haven demand as something like US Treasuries. Moreover, when bond trading is volatile, lenders are less willing (and able) to pass along the improvements implied by trading levels.
All that to say the mortgage market needed some time and some extra cushion from higher bond prices before lenders were able to make bigger moves toward lower rates. Today was the day when those stars aligned.
To be sure, the average conventional 30yr fixed rate is still much higher than it was 3 weeks ago, but it's now lower than any day in between. Pricing is very stratified, depending on the lender, but the average lender is an entire eighth of a percent lower than Friday. That's a big move in general, but it's an exceptionally big move in the context of recent volatility.