for many of the sports they don't do it for the money, because there is very little
I agree that a lot don't do it for the money, and more for the glory and being the best. I don't know in your country, but there is good money involved in some countries. In the Philippines, medalists get a lot of rewards from private companies. There are sums of money, house and lot, endorsements, and other things. So there is good money to winning.
As for holding qualifiers, I think it is necessary. A person's skills and abilities could have diminished after 4 years, or within even a span of a year due to injuries. Athletes wanting to go to the Olympics need to treat these qualifiers as if it is the actual thing. So if they fail in the qualifiers, what's to say they wouldn't do poorly in the actual Olympics as well.