Presumably it has to do with methane from cows. This is now beginning to be mitigated with seaweed feed. Otherwise, land-use for cows has been decreasing in the U.S. despite population increase. It has, however, increased in Brazil owing to soybean crops used for feed. That has been contentious because of encroachment into rainforest land, but it's not clear the scope of it really matters. The most cut and dry benefit to alternatives is far and away animal welfare.

When it comes to just flavor profile I'm not surprised there would be some disruption (good use-case for ice cream, a junk food), but there's no real sub for the animal protein (if you care about that). And in terms of calcium content the products are just fortified, so you're paying a premium for what might as well be a supplement.

I've tried a few yogurt alts that tasted alright, and the nutritional content seemed satisfactory fitting into my diet (though nothing for good for kefir yet). Of course I'm not keen to spend more on plants than I would for an animal product, and one wonders how green something can be when it includes coconut transported via cargo ships and highly refined ingredients.