That's really annoying. I use all the lenses in the Zeiss Batis line, some for over 10 years now. Luckily, they've all worked perfectly so far, even though I haven't always been gentle with them over the years—photographing in rain or heavy snowstorms, and the lenses have been exposed to saltwater and very fine sand during a sandstorm. Even with the oldest lenses, I haven't found a single speck of dust inside, which suggests excellent weather sealing. With other lenses that I've also used for just as long, dust has gradually accumulated inside the lens barrel. I honestly believe these Batis lenses will serve me well for another 10 years. Maybe you just had a run of really bad luck.