Because clients are run by idiots. Sorry, but it's true.
Clients are run by people who look at the funny acronyms and you can watch their eyes glaze over. If they know anything about it, they will know that there are keys and these keys depend on how big the number next to them is. That there are symmetric and asymmetric keys and that 512bit can be a LOT if it's symmetric and insignificantly little if it's asymmetric is already something you won't be able to teach them.
So configure your servers, people. Configure them to ONLY accept sensible ciphers. Yes, that means that people with Internet Explorer 5 might not be able to use your page. Then inform them to fucking get a browser that was made in this millennium! These people are a security risk and bluntly, if you want to do business with them, you do not want to do business with me.
Or at least I don't want to do business with you!