That's not technically true. When it was originally released in August of 1965, the only engine available in the Ford Bronco was a 170 cubic inch straight 6.The bronco has always had a V8 in it
The 289ci V8 was added as an option in March of 1966, 8 months later.
The third, fourth, and fifth generation Broncos (1980 through 1996) all used a 300ci straight six as the base engine, although V8s were available, and it wouldn't surprise me if the 302ci and 351ci V8s had a higher take rate over those years than did the 300ci sixes.
If we're being really picky about what the Bronco should have just because it "always has" (also not technically true, the '78 and '79 only had V8s), then we should be demanding a naturally aspirated inline 6 cylinder.
But we're not any more likely to get that in the 6th generation Bronco than we are to get a V8.