They do it to dogs too because they think torturing them makes the meat taste better but they're used to bugs cooked in poop oil so anything tastes good to them. It's scientifically proven it does the opposite and makes them release a bunch of stress chemicals that makes the meat bitter sour and bad.
Some results from a search:
Stress causes the release of adrenaline and cortisol, which can make meat tough, tasteless, and high in pH.
Stress uses up glycogen, a stored energy source, to create adrenaline and cortisol. This means there's not enough lactic acid produced after slaughter, which can affect the meat's quality.
Stress can cause the body to accumulate hydroperoxides, which break down into aldehydes and ketones. These chemicals are responsible for the bitter taste and foul smell of bad meat.