1) they only carry 1
2) they throw it on a significant number of holes per round (more than 1/3)
so basically, you just learned the lesson of why you don't ever carry just 1.
let's say you carried 5. it would probably take 3 months to get any noticeable change out of any one of them.
But how often do you hit trees with them?
i hit plenty of trees as i play wooded courses. i also play w/ a practice mentality, so i throw a lot of shots that hit stuff i'd rather avoid (e.g. asphalt because i took the hard line over a parking lot).
the farther you can throw, the harder you drill trees as well.