I think this is a good example of the practicality, and the style (BOOM!) of The Art of Electronics. This shows very nicely how failing to put a diode across a relay coil can get you into a lot of trouble. Boom, indeed.
“The Art of Electronics” #4 Boom! Putting Diodes Across Relay Coils
Could never figure out why not build the diode into the relay during manufacture?
There are some selected Omron and others that do have the built-in or “catch” diode. See: https://www.ia.omron.com/support/faq/answer/36/faq03676/ But, true, the vast majority of DC relays do not. For DC relays, having it built-in could help reduce EMI during the switch transient, by have a slightly smaller current loop or “antenna” if done properly. 73!