I also only have public information, but the sense I've gotten was that Twitter had an embarrassing problem, with high-profile accounts being compromised, and J

I also only have public information, but the sense I've gotten was that Twitter had an embarrassing problem, with high-profile accounts being compromised, and Jack personally hired Mudge to fix it, with Mudge reporting directly to Jack. This set up Mudge to essentially be the parental supervision for Parag, which chafed / pissed Parag off. Then, when Parag became CEO, Mudge was out, having not accomplished much because Parag was actively hostile to the interference. Again, conjecture based on what I could extract from the froth, but mundane enough for me that alternatives (shocking displays of X) start requiring extraordinary evidence.