Why food is still tasty?
Things are not fundamentally tasty or disgusting. A dung fly loves that taste of dungs while I personally prefer the taste of an apple and my dog prefers the taste of duck fat. A classic example is the gene family TAS2R and the evolution of bitter taste in rodents and primates.

Predator (incl. herbivores) evolves as to like the taste of what he should be eating (Carlsson et al., 2009). Preys (incl. plants) can eventually play out with their taste though, trying to either taste bad to avoid specific predators or taste good to attract specific predators that may disseminate their seeds. I have failed to find evidence that plants can deceive animals at being more tasty than nourishing but you might still want to have a look at Dethier (1980), Sorensen (1983) and Goff and Klee (2006).

One could therefore expect an evolutionary race (red queen) between preys and predators upon how they taste. It would likely be a rather complex race as most species have several predators and several species they prey upon. However, such race on taste would work only if plants can deceive animals which I failed to find evidence for. Arms race for toxic compounds relating to evolution of taste in animals are very much known though (Edger et al., 2015).