The current regime of near universal caloric surplus is not something our ancestors ever faced and evolution left us very little tools to deal with instinctively.
This depends on your ancestors. Demographics with a long history of agriculture are much less vulnerable to diet-induced diabetes than, say, native Americans are.
Some people will eat to gorging when faced with more food than they can eat, and some won't.
Diabetes and Mexicans: Why the Two Are Linked
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932342/
Diabetes Mellitus: A “Thrifty” Genotype Rendered Detrimental by “Progress”?
For example, if you suddenly require 5000 c/day, you cannot simply eat more pizza, MT Dew, etc. You have to eat 5000 c/day of nutrient rich food. Your muscles do not only require calories. This is actually very hard to do (imagine how much actual food volume you have to process)!
You also need many more macronutrients to keep things going (all that extra food needs to be processed), and clean (significantly more waste byproducts produced).
Your cardiovascular system needs to grow in conjunction with the extra muscle -- it must keep up. As does your skeletal (bones, ligaments/tendons).
Lots of pizzas also have meat toppings as well.
Depending on what kind of pizza you eat, the cholesterol may also not be very high.
But I think this comment is overestimating how many calories you'd need and how concerned you'd need to be about nutrient balancing, even on a fairly intense training program. Most people, in their first few years of weight lifting, aren't going to need much or any increase to their daily calories that they wouldn't come by naturally from getting hungry due to the exercise. For people who want to lose some weight, moderating the size and frequency of meals and cutting out obviously bad food will have the quickest and most visible results.
It's far more important to just hit the weights consistently. That's where you get results. I started about 2 years ago and dropped about 40 pounds without ever worrying about the diet side of things or counting calories. The only real changes I made were to start taking a daily multivitamin and to make an effort to avoid sugared soda, fruit juice (has a ton of sugar), junk food, etc.
"... [I made] an effort to avoid sugared soda, fruit juice (has a ton of sugar), junk food, etc."
Important contradiction to point out there. I'd say you did worry about the diet side of things given the effort to avoid sugar and junk.
It's a common and widely accepted saying that "abs are made in the kitchen." That's to say, if you want to loose weight, you must change your diet. A few days of cardio or strength training per week won't make up for a bad diet. In fact, if all you're trying to do is loose weight, you're better off working on the diet than the strength training. You could end up being very discouraged if you go the opposite route. Ideally, do both and you'll see results very quickly. But think diet for fat loss, strength training for...strength.
When it comes to diet, I am an unashamedly lazy man. Lifting the weights is tough enough as it is. I'm not going to live on oatmeal or kale, count calories, or any of that. That just sounds awful.
What works for me is cutting out things that are obviously bad for you: too much sugar, too much salt, comes in a can or a box with a long list of preservatives, etc. Simple plans are easiest to stick with, after all.
Just a little joke, there.
Pizza and soda are nutrient rich - macronutrient-rich, that is.
If you're getting the right number of calories, and the correct ratio of protein, fat, and carbs, you can mostly eat whatever you want.
Relevant: "Food Composition (Nutritional Priorities with Dr. Israetel)" https://www.youtube.com/watch?v=qwGspJZt1kE
If muscle isn't needed and used, it's expensive to maintain.
(But it could be many other reasons too when you factor in sexual selection, etc.)
That's a great research question. Normally, the body tries to maintain a happy "set point" of fat. However, different genetic populations (who may have historically gone through more famine) are more inclined to save fat than dump it relative to others.
Researchers suspect that there is some mechanism that may be going awry due to our modern diet/lifestyle. Fat makes a protein called leptin; the more leptin in our body, the fatter we must be. So why is our body not properly measuring how much leptin is in our bloodstream and thus thinking it is skinnier than it really is?
Answer that and you will both win a Nobel Prize and become a very rich person.
you might know that this calorie surplus will last "forever" but your body doesn't so to speak so it's choosing a safe bet survival strategy-wise.