$80 is the initial buy in, not a yearly fee. For instance, I purchased at $51.50 in 1992, giving me roughly 49 yeears to use my points...so, $51.50 divided by 49 = $1.05 per year. Now add current dues (estimate 4.25) for a total of $5.30. Renting at $12 for 300 points would gain me an annual profit of at least $2000. That is why some people rent. Personally, I usually bank a few points every year, and when I have extra built up, I invite friends/family for free...I don't rent out points. But some people bought a lot of points for the sole purpose of renting.
Others, as the previous poster indicated, rent to be able to pay cash for other locations or cruises.