What is the real reason Washington DC does not allow skyscrapers to be built (hint it has nothing to do with the Capitol)?

Washington DC has a height restriction on buildings that dates back to 1910.

It's something of an urban myth that the reason is so that the Capitol Dome or the National Cathedral are both visible from distance.

Instead:

In Washington, D.C., the 1910 Height of Buildings Act actually takes height from the width of the street on which a building is situated. So it's an urban design principle.

Effectively, the cap on commercial buildings is 130 feet (40 meters) or 11 stories. Wider streets have taller buildings while those in narrow streets have to be shorter. The only exception is Pennsylvania Avenue which allows some buildings up to 160 feet (49 meters).

https://www.npr.org/transcripts/317394811