I'm not entirely sure it made sense even then. I completely understand the point (knowing the AR allows one metric to consistently compare and derive the other dimensions) but in my opinion, diagonals became ubiquitous because when looking at TVs, bigger was typically better in the consumer mind and the diagonal is of course one of the largest justifiable dimensions they could plaster over the product and cheaper to print/advertise (less text to put on boxes and flyers).
I think we were handed diagonals in the same way prices are often advertised at near complete fractions of dollars ($9.99): it projects more value to the average consumer's perceived value than it actually provides.