I think you're possibly defining 'I'-ness the wrong way.
Your statement, "I have never met an easy-going 'I'" implies that either you don't know a lot of people (which would make me suspect that you're an introvert), or are using the wrong criteria to define 'I'. It's the same as the 'Loners are freaks' scenario you keep seeing. In these, if somebody has any outside connections whatsoever, they are no longer a 'loner'... even though there are a great many loners who do, you know, know a few good people.
A wild guess says that you know more Is than you think but don't identify them as Is because they don't fit the pattern you've 'noticed' of being 'cranky.' Because of this, the assumption perpetuates in your mind.