In the pre-internet days there were a number of broadcast trade journals, and used equipment brokers. If you were going to home brew a simple automation system, you looked around to see what was readily availible, and cheap. It was easier to buy the same repair parts for a dozen of the same machines, and you could scrap a dammaged deck for motors and heads, or other parts to keep the rest running as they aged.
By the time thay became too expensive to maintain, computer programs on computers with a bank of SCSI drives, or remote controlled multidisk CD players took over. Today, it would be cheaper to have a rack full of cheap computer CDROM drives, instead of $1500 six disc machines made for broadcast use.