I think it's worth remembering that fermented milk products are very ancient foods and have been around long before refrigeration and very often in the hottest climates of India and Persia, simply because they are ways to extend the useful life of the milk. What you get depends on the species of bacteria that dominate. The desirable ones are desirable on account of the taste and texture they produce. The bad ones are bad because they taste bad. (Although what tastes "good" and "bad" can be far from universal.)
Once the native lactose in the milk has been consumed and lactic acid produced, the product is pretty stable. Mass-produced products begin with pasteurization to kill any native bacteria before the working bacteria are added. So there's not much undesirable bacteria left and not much food left for any bacteria. Yogurt is produced at about 112F, so being left in a hot car for a while is not going to do much to something where the lactic acid production has already run its course.
Cream cheese and sour cream are produced in similar ways and are similarly stable, although cheeses may suffer in physical ways under heat.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen