TBH I stole that from an article I read a while ago that I can't seem to Google now...
You can't liquidate any built up equity either, since you probably need income or assets to get a rental or equity loan. So it's completely possible that you lose any built up equity in the event of a foreclosure too.
I think, if anything, this position is actually supportive of making an educated rent vs buy comparison, by discarding any kind of "investment" potential on the buy side.
Others might have other reasons for similar state.
This is more meant to attack the idea of a primary residence being an "investment". If people insist on calling it an investment, then it's fair for me to insist that it's only covering a short position, because you need somewhere to live.