I am not sure that is true as even for stocks, on the other side you have asset managers, hedge funds or insurance companies who participate both in the primary and secondary markets. Of course, you will have similar bubbles forming in stocks than you have in property. But overall it is a way more productive investment.
Bonds barely trade on the secondary markets. When you invest into a fund that buys bond, it's pretty much 100% primary market (i.e. new issuances).