One thing I don't quite understand: Why not combine the testing with the using? As in pretty much everyone who wants to, can apply for the vaccine testing, but

One thing I don't quite understand: Why not combine the testing with the using? As in pretty much everyone who wants to, can apply for the vaccine testing, but they then are gonna be monitored. Based on my current understanding, they pretty much cherry pick the testers, so they only have a small group.