for the voltmeter style ones its partly due to them being inherently so long lasting, the only thing that can really fail in them is the bearing for the pointer, and those $80 ones tend to use a brass bearing that will happily out live you only having to handle a few grams of weight, whereas the chinese ones use a plastic bearing that will last long in a proper 15-25 degrees C min-max lab., but get to cold and it will go brittle or too hot and they will suck up a few of the volatiles in the oil and fail within 5 years,
So if you want them to last in a warm climate for decades, get the cheapies, wash out the lubricant and use one that is plastic friendly long term, its common that if a product doesn't fail easily they either make it so or charge more to cover the decreased long term replacement sales,