I think there are two main reasons for the problems of receiving SAQ in North America today.
The first reason is the receiving antennas used. As radio amateurs today can use antennas not bigger than their own garden, the antennas for receiving commercial telegram traffic were huge. The commonly used antenna was the Beverage antenna. The antenna in Riverhead on Long Island outside New York for receiving European transmitters was about 14 000 meters. It also had a facility to cancel local noise from nearby transmitters, thunderstorms and statics. More information on the Beverage antenna can be found here: http://www.nrcdxas.org/articles/WaveAntenna.pdf
The second reason is that the amount of man-made noise has increased over the years. Power lines, railways, washing machines, dimmers, all contribute to an increased noise level. At least in Europe, it seems that local noise is a worse problem than low field strength when receiving SAQ.