Auto manufacturers were still picturing men wearing hats and mentioning room to wear a hat in sales brochures until the very early sixties. I don't recall having seen a post '63 automobile sales brochure with men pictured wearing hats, unless they were chauffeurs or wore hard hats, but in '58 almost all the men are portrayed wearing hats. After 1960 hatless men outnumbered men with hats in automobile advertising and sales brochures. Judged from this between '59 and '62 hat use may have fallen off very steeply. Rightly or wrongly I tend to think that advertising and brochures of this kind, while they may not reflect the reality of society, do tend to reflect an idealized norm of sorts. Even if most men no longer wore hats in '59 the idea that a man "should" wear one seems to dominate advertising for year specific items like autos. In '61 it must have not been the ideal any longer as only a few men are pictured wearing hats and most are lidless.
John Thornton