Even if true (I know many professors who did postdocs), it's not clear what you think this proves. Faculty slots are very scarce and most newly graduated PhDs,

Even if true (I know many professors who did postdocs), it's not clear what you think this proves. Faculty slots are very scarce and most newly graduated PhDs, even very smart ones, do not have "faculty job at a desirable institution" as an option immediately available to them. So they are left with the choice between postdocs and industry. Most choose industry, and it's not hard to understand why.