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.

Yep - medalists do. But, there are only 3 medals. What about the 50 people who don't medal, but put in all that work over a lifetime?

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.

For sure - but they have other track events all the time. In the US, the qualifiers are the thing, so one slip there and it is over. However, in most countries, the olympic committee chooses the athletes, which means there is a chance that they still get chosen. But, this has its own problems.