I kind of thought it was a given that immunity has been shown to wane after 6-8 months, and the 3rd shot helps boost antibodies back up. However, I took it that what's best for me isn't necessary what's best for thee.
In other words, boosting me from 50%-60% back up to 95% is considered less helpful than giving those shots to the unvaccinated, because of mutations and hospital resources. Especially while severe illness remains relatively low for the vaccinated. Interestingly enough, I'd bet 99% of the people with any influence on this decision have already been boosted, or will be very shortly.