For over a decade, the Internet believed the problem with ECB was that you could see penguins through it. Implementors looked at that, said "I don't care if you can see penguins through this", and plowed ahead. In fact the real problems with ECB are that you can rewrite the plaintext and, in many common configurations, decrypt it outright --- the same insight got us the BEAST TLS attack.
A block cipher in ECB mode is a substitution cipher, with all the weaknesses that entails. A substitution cipher with a lot of bits per symbol.
Do any specific books come to mind for you as recommended reading for those looking to learn more?
JP Aumasson's "Serious Cryptography" and David Wong's "Real World Cryptography" are good starts.
Cryptography Engineering is the classic. Serious Cryptography is also good and more recent.
I liked Cryptography Engineering ("Practical Cryptography") but it definitely doesn't hold up; it was obsolete by 2010. You'd get yourself in trouble implementing from it today.
Serious Cryptography by Jean-Philippe Aumasson.
I recommend going through the CryptoPals[0] challenges. I'm halfway and they really beat into you the problems with ECB.