A solution expert usually brings a baggage of knowledge of previously working solutions in the problem space, knowledge that has been acquired over many months of hard work

Short gigs where you being in a solution, point a team/company on the right direction and then jump off compensate for the accrued knowledge transfer more than for the hour worked

Think of it like a top end athlete, they aren't paid for the few hours of play, but for the years of training that keep them competitive