Standards companies charge for their work because that his how they stay in business and fund continued development of the various standards that they sell.

No one really expects the average person to buy these documents. The target market will be the bike brands like Trek and Giant and so forth. Lawyers might by them in support of litigation. Journalists might by them for research. And I'm sure the occasional enthusiast buys a copy now and then.

The standards themselves have no legal force, but I did read just now that the U.S. Consumer Product Safety Commission (CPSC) participates in the creation of the ASTM standards involving bicycles. I suppose it is possible that a law or a CPSC rule could incorporate a standard by reference.

There's value in the standards. Imagine you wanted to create a new brand around bicycle forks. You had better have some design standards in place. Paying the ASTM for theirs is a lot less expensive than doing research from first-principles and developing your own standards from scratch. And if you did develop from scratch, you'd want to check against work from ASTM and other standards bodies to help ensure that you have not overlooked anything.

If you built and sold a fork and were involved in a lawsuit, and you could be shown to have completely ignored the available standards, then that probably would go against you in a jury trial. So there's an element here of covering one's backside, but one can also benefit from the work of others who have gone before.

I can't shed any light on your frame and what it's capable of, because you haven't told us what it is. You would probably do better in asking the brand -- Giant, Trek, etc. -- about what their frame is capable of.