Vaginas are come in all shapes and sizes; there are different depths and widths for every lady and the channel can have a curvature as well. A tight lady doesn't necessarily indicate that she is not aroused or is virginal and a loose lady doesn't mean she has had too many partners or a baby. It's just anatomy we have no control over.

A lady being aroused but not wet could be due to products being used like soaps or creams, medication, low estrogen, or even medical conditions.

A very common culprit for a lady not being able to get wet is low estrogen birth control pills. I encourage ladies to avoid these at all cost. I was on them for 3 months and I damn near mummified I was so dry and they fucked up my skin and attitude too. IUDs are the way to go!