Credit Unions vs. Banks is a lot like Exchange Traded vs. Mutual Funds. All the advantages/benefits are on one side, yet most of the money is on the other.
Related: I looked at Vanguard's compare/contrast between ETFs and mutuals...it seems that the "difference" is mostly the name (and which one your plan lets you get).
Finance is weird. There is no reason for most fees/costs other than scamming/siphoning and other fraud, yet the vast majority of people (really, money) who participate do so via the worse options. I don't get it. Why would any sane person keep their paycheck at Chase when some local credit union is going to give them better rates and service?