Rotting roots (or leaf base)
Over time every Sanseveria I have had has lost a goodly number of leaves. From root rot, or whatever, but the leaves just pull out with no resistance. These are in the soil they were purchased in. I water them once a month or so. One...around 10 years old...finally had to be pitched there were only a cople leaves left.
It would seem that the problem is due to either too wet, or too dry soil, or disease. Any insight as to how to avoid this would be appreciated.