Unfortunately, your concerns are very valid.
Pieter Hintjens has great post on that, claiming that "AMQP/1.0 will go down in history as a prime documented example of how to fail a standardization effort and hurt a lot of people in the process."
To your question: "why would I favour a message broker that is AMQP compliant over one that is not?" Definitely not because you get the option to change your message broker provider, as it is now not required. There are only two situations, I would think of favouring AMQP message broker:
1) You are already used to that and have that broker easily available
2) AMQP still brings the advantage of having clients available in multiple programming languages. But STOMP would serve here too.