https://en.wikipedia.org/wiki/Human_jaw_shrinkage

The main contributing factor to the recent increase in malocclusion is widely considered to be due to a sharp reduction in chewing stress, especially during critical periods of craniofacial growth.[10][1] Experiments done on non-human subjects have shown that induced nasal blockages and/or dietary changes earlier in life lead to maladaptive morphological change in their jaws, intended to simulate what we are observing globally in human children.[4] Significant craniofacial changes due to diet have even been experimentally shown in pigs during development; researchers fed groups either a hard-consistency diet or a soft-consistency diet, for eight months in total.[11] Drastic differences in jaw and facial musculature, facial structure, and tooth-crowding were observed; researchers directly related the findings to what we are observing more in human populations.[11]

so too much damn baby food?

because people with very bad teeth survive nowadays

Our food is way softer so we don't chew enough to maximise the growth of our maxillae and jaws.

We eat soft, processed foods now. We used to graze and chew constantly, which helps the jaw grow properly.

I think I’d read before that it was because most of our foods now are soft foods so our teeth/jaws are not as strong.

Sugar content of our food is one of the reasons I read before as well.

im p sure it has to do with stuff being easier to eat. we dont have to work with our jaw to tear or crush difficult foods since everything is processed or we have tools to make it easy. our jaws are underused, so they develop to be smaller than theyre supposed to be, and our teeth get crowded

Everyone who's replied to you so far are wrong and speculating. The real issue is actually lack of nutrition and exercise for the mouth. We're not growing our jaws out quite right while our teeth are coming in.

Before we cut our food in perfectly sized bites with utensils our ancestors used to do it by biting into large pieces of food with their front teeth. That would wear them down evenly to form a nice flat bite.

I wouldn't be surprised if that's the skeleton of someone who died way younger than we think as well.

Something else that affects our teeth (though I'm not sure if it affects growth) is sugar consumption. Our ancestors had very little access to sugar or even spices. They ate things like meat and veggies plain. Back in prehistoric times, this meant they wouldn't have to brush their teeth, since the bacteria in their mouths wouldn't have produced plaque.

That's why a lot of human remains of 80-year-olds from 20,000 BC have perfect teeth or only a few missing after those teeth got knocked out by getting hit in the face. If you're ever stranded on a deserted island, you should avoid eating all those coconuts and bananas with every meal.

We eat shitty food