It is understandable why states might be interested in regulating the Visible Light Transmission of the tinting on the front windows -- to make sure the driver could be identified in case of accidents / hit-and-runs / other issues, by both the general public and the police. This is, apparently, why some states, like California, dictate that VLT of the front side windows must not be below 70%, whereas all other windows -- back side and the rear one -- could be as tinted as one pleases, e.g., even limo-style 5% or below is acceptable.
However, other states seem to regulate all windows -- front side, back side, and the rear one -- and many mandate at least 35% VLT on all of the windows, whereas some north-east states like New York even go as high as 70% VLT on all windows, which, frankly, doesn't seem reasonable at all. This is especially interesting in light of some vehicles not having any back side windows, nor the rear window.
What legitimate interests do the states have in regulating back-side and rear windows? Are those laws enforceable? Especially, as potentially a special case of the Window Tinting rules and laws in visiting jurisdictions question, would someone with a 70%/5%/5% tint and California or Texas licence plates, where such tinting is legal, can be legally forced to pay fine and/or remove the 95% tint from the back-side and rear windows in a state where it's supposedly not legal? What if it's a local vehicle?