Not including fees in the nightly rate makes sense as some are fixed rate, and having the option to see the cost for the total stay (including fees) solves the problem.
If you search for an area without dates, it comes up with some arbitrary dates and applies the fees and displays per night cost accordingly.
So it's technically possible. They just don't want to.
It can be done. Marriott show the total including taxes. Mind you, this was as a result of a legal settlement, so they get no credit.
At least on booking.com it depends on what settings you have.