He abdicated the responsibility as he from the beginning didn't have any power (always the single dissenting vote). There also isn't much leadership to provide if everyone else in the "leadership circle" is on a different frequency, or otherwise you are just a rogue actor that will quickly get kicked out.

If anything the time for him to leave would have been when he stepped down to be an engineer. I don't think there is anything wrong with laying your reasons for leaving bare, especially when many people will come asking why one of the co-founders left.