Interest rates have been on a downward trend for the past few decades. This is a new thing, that has not happened before. The Fed seem hell bent on making sure that there are no deflationary recessions anymore, and i think that is the true cause of the long term decline in interest rates.
One of the results of this trend is the hyper growth in asset prices. Reduced interest rates dictate a reduced time value of money, and higher valuations. This rewards the owner class with increased wealth, and doesn't do anything (and well actually harms) the rentee class, which pays the same rent for a home.
The problem is that this is not sustainable. I'm not sure if you agree, but we cannot keep decreasing interest rates forever. It would have to slow down and stop one day. What that means is that some future (or present) generation would not be rewarded with increased wealth that past generations have enjoyed. Essentially in order to fight deflation, the Fed has borrowed immensely from the future to openly gift wealth to the present, making the future less rosy.