I think it has more to do with the fact that the manufacturer has enough data and information to know that a bmx is a kids bike for the most part and the majority of kids need a bmx that is strong enough and that not every kid will be doing the stunts/tricks that a professional does. That a bmx is a 20" wheel for the most part, will be outgrown and the bike will be replaced too. Granted, the chromoly frames are nicer, but a company wants to sell more product for brand name recognition rather than fewer.