If a hobby declines in popularity, it also can become more expensive to pursue, as economies of scale hurt--which makes it more expensive, which makes it less appealing. One thing that surprised me then and now: No inexpensive Revell models of Texas and New York. Both are high population states, leading to a natural base of kids that would grab them preferentially, as well as having Texas as a memorial. (They would be one kit with different labels; back then, the USS Pennsylvania and USS Arizona kits were the same, with different decals and boxes. Occasionally, one different sprue of parts would be included for the minor variations, but sometimes, both would be exactly the same, even if the ships were different.)
Back when I was a kid, parents remembered the battleships.
Modern first line warships don't have as many neat guns bristling every which way--they don't have that aura of menace that older ships did. Also, some of the less costly models are available--but not in the local Rich's, Woolworth's, Anne & Hope, or Zayers--you need to go into a specialty hobby store or online. Thus, impulse purchases, where the kid is looking for toy cars and sees the battleship, are less common. (Or just dragged into the store when Mom or Dad is looking for not-fun things, and gets loose in the toy department!)
As for the anti-war, I was a kid in the 70's, and battleship and other war models were very available.