Mortgage rates are increasing in recent weeks despite the Federal Reserve's decision to cut interest rates last month for the first time in four years.

Most outstanding mortgages have a 6% or lower rate, which creates a " lock-in effect " for many current owners who don't want to swap a low rate for a higher one. This could limit homeowners’ willingness to sell, slowing or stalling the housing market.

The average rate on a 30-year mortgage in the U.S. rose for the third week in a row, reaching its highest level in eight weeks. The rate rose to 6.44% from 6.32% last week, mortgage buyer Freddie Mac said Thursday. A year ago, the rate averaged 7.63%.

On September 18, the Federal Reserve kicked off the cutting cycle by reducing overnight rates by 50 basis points. Since then, mortgage rates have gone higher. This is not obviously an intuitive thing to happen.

The Fed announced first rate cut in a long time last month, but the mortgage rates have continued to rise. Why is this? Here's why.