Why does a punch to the body make you more likely to get countered in your face?

Because it conditions your opponent into expecting a body-shot, so they anticipate and prioritise defending to the body so might drop their hands or might just not notice when the trajectory of your punches change because they've put more attention to body-punches. Case in point, Canelo Alvarez loves to drill a particular combination onto an opponent to condition them to expect it (double jab followed by a right hook to the arm is a personal favourite of his) then will change the combination mid-way through the fight to catch his opponent since they've begun to expect the same combo (e.g., changing the right hook to go upstairs, or throwing a straight right upstairs). It's how he dropped Jermell Charlo and he did it a couple times against Callum Smith.

EDIT: misread the post title, thought it was about how body-punches set up head punches.

 

Your head has eyes. Your body doesn't.

If you throw a punch to the body, your opponent can see it and react effectively (punch back).

When you punch someone to the head, even if it's a jab, it can affect their ability to see what is coming next.

Which is why fighters are taught to throw combinations to the head. The first punch, even if it isn't solid, tends to blind the opponent to the shots coming right behind it.

And the punches that hurt worst are the ones you don't see.

 

Yup In my experience as a boxer, body shots were safer. When my eyes would swell up or I’d have blood in my eyes, body shots were always “safer. The body is definitely a much easier target. You can’t move your body like you can your head.

 

Because body shots require more skill to be competent at them. You usually have to get closer, drop levels, set it up so there aren't any obvious tells and be aware of positioning to throw them properly. Neglecting these while going downstairs will increase your chances of getting a hook, uppercut or even straight punch in return.

I'd say there's some truth to it. An aggressive fighter looking to break down his opponent would take more risks and leave themselves more open in their winging than a classic boxer who is stingy with their power punches.

 

I meant that the Ali type boxers were less likely to risk putting themselves in that kind of situation than the rough and tumble kind.

 

Because your hands are significantly lower