A general rule of thumb is sewing machines store well any place humans would "store well"
Attics get Extremely hot, basements get extremely cold. few folks would want to live in a basement or attic. Most primary dwelling spaces are moisture "managed" but most outlying spaces are not.
The older the machine, the more sensitive the finish is. 10x was spot on about shellac vs enamel.
Really old machines have polished steel components, vintage machines tend to be nickle plated, while newer machines typically have hard chrome finish to the metal bits. ALL of that makes a difference in its requirements for care and longevity.
Dull metal rusts easier than polished metal, polished metal resists rust better than brushed or satin finish metal due to the reduced surface area of polished metal