2 cents
1) Myles really did want out, and went to a decent amount of effort-ing to do it
2) AB told him, look, we can't do it financially w/o crippling us, and it can't be to a contender, due to poor draft capital return a good team would have to offer. The cap guys said it'd mean trading Ward and Njoku, telling Bitonio no-thanks, and cutting Conklin. That, plus the loss of Garrett, is a complete gutting of cornerstones.
3) So, he said, pay me then, "I'll have to trust you're going to continue to go full-go", and I want a "no trade to football Siberia" clause
4) He'd actually be tradable, financially, after 2 years. Perhaps there was a "give us 2 years, and if it doesn't work out, you can always seek a trade then, and you'll have control over where you go, with the no-trade clause". And to all of that, Myles acquiesced.
5) AB would agree to this because frankly, if he hasn't turned the team around this year or next, it's probably not his problem anymore. He's gone, and Garrett's demands would be the next GM's problem.