It looks like that is a conversion and retrofit of ships that were already unmaintainable: https://washingtonstatestandard.com/briefs/conversion-of-was...

Modernizing all the control systems etc is the nightmare. The ferries were already electric- all ferries are; they have diesel engines driving generators which drive electric motors. They still have the exact same generators running the same motors. The batteries are installed and ready even though they won't be used until the port is electrified years from now: https://www.youtube.com/watch?v=hkgT9Z8Z2RU

Sure but you have to think of the entire system which includes staff, training , charging infrastructure, power supply, possibly fuel for the charging infrastructure, backup/redundancy, maintenance, parts / distribution etc. An entire infrastructure network that had been operating for decades.

Diesel is more than just fuel, it’s an entire system.