$4,000 may seem like a lot of rent for that house but by Cambridge standards it is not. There are a lot of apartments that rent for more than 4k. We’re assuming Gates pays the rent. Maybe his foundation pays most of it.
There’s probably not a house in Cambridge to be bought for less than 1million. The assessed value of Gates’ house is $1,283,100. On the open market it probably would sell for more but it is owned by Harvard. Gates has a deal.
With your explanation it’s easy to see why it rents for that and like you say, this foundation probably pays for much of it.
I know, I thought it was a deal too for the size of the house. My daughter rents a small 2 bedroom apartment near Central square and she pays almost $2000.