Rapidry was a VERY important selling point back in the day.
MANY families did not yet own a clothes dryer, and less time on a clothes line made a BIG difference---especially because families used to be much larger than they are today.
The people who used clothes lines and traded in a Unimatic for, say, a '63 Multimatic were quite vocal in their dissapointment.
Frigidaire got the message and when the Rollermatics came out the option was back.
By the time the 1-18's hit the market, Frigidaire must have figured out that most folks now had dryers or it was just easier to sell them by then. AND a 1-18 dryer is a GREAT dryer.