Getting some level of management and learning there is no authority of responsibility given to the role. It's just another type of task handler. The disillusionment is common when people crave responsibility and realize it isn't forthcoming.
Had you been granted the authority to oversee a critical responsibility/project/initiative you might have been imbued.
It's very exciting, like a drug, to be given responsibility for which you know that you are immediately shit canned (by your friends no less) if it doesn't go well or rewarded handsomely if you get it over the finish line. You have to hold key peoples' (founders/investors/executives) trust to get those roles because your success/failure ripples into them right quick.