Few people could afford the expensive equipment and there really wasn't much to write about. In the last couple years, many new low cost SSTV systems have become available and tens of thousands of hams have discovered the fun of SSTV despite the difficulty in finding information. I have no idea why the American publishers continue to ignore it. This allowed an image to be painted on the screen over a period of a few seconds. When memory chips became affordable, scan converters became feasible.
Scan converters translate one TV standard to another.
In the other direction, it stores an SSTV image in memory and allows it to be displayed on an ordinary TV set. The latest trend is to use a personal computer, software, and an interface attached to your transceiver. This is much less expensive and much more flexible. Some Multi-mode TNC's can handle SSTV with optional software. You can even use a Sound Blaster with the Slow Scan II software.