When you join you purchase points for $84 each. They are then yours for the next 39 years, and you receive a new allotment each year to use. You only pay the annual maintenance fees that average about $4.00/point.
When people rent points they get to use the points for 1-time only.
For example, you purchase 150 points for $12,600 and pay $4.00 point annually for the next 39 years which is $23,400 so your total investment for 39 years is $36,000.
Over that timeframe you had the use of 5850 points. (150 x 39)
If you rent points at $10 each, 150 points would be $1,500. Do that for 39 years and your total cost is $58,500.