Sorry you think the cloth covers are a gimmick. I've found them quite useful and definitely not a gimmick for me. Leaks can be caused by the pressure being too high also, some leakage is expected and normal according to my sleep medicine care team. The leakage has not affected my AHI either way. If you have any kind of silicone average or just don't like the feeling of the mask on your nose or face, the cloth covers can help you when using the CPAP. More people quit using a CPAP just because they hate the feeling on their face. I struggled with that for over 4 months and thought about quitting the treatment prior to finding the cloth covers. I can't say they are for or will work for everyone, but if you are struggling to keep using a CPAP, it's another option and it's not expensive.

Perhaps that was your experience. I know many who have found that using those covers prevents 'rain-out' because they help to insulate the hose against cool bedroom air...which most of us prefer. In my own case, I simply cover my hose with my cover. I place my sheet across myself, then lay my hose across my midriff, and then place the cover over the hose. The weight of the cover helps to keep the hose in place, and the cover serves the same purpose as the cloth 'sleeve'.
Improper fit, inappropriate geometry, unsupported hose, displacement/deformation of the pillow/mask, these all contribute to leaks.