Because they didn’t call them food allergies back then. Things were “too rich for me”, or “didn’t agree with me”, or if you were uncouth “gave me gas”.
Or *choking to death on a peanut caught in the wind pipe*.
Notice that you NEVER hear about that any more.
I wouldn't be surprised that all those cases of *choking to death on a peanut* was actually anaphylaxis closing up the airway and they just didn't know it.
I think that you are definitely on the right path with this one. But I would add that most of what people are claiming that they are allergic to are really not true allergies... it is a misnomer. There are some foods that their body may have a difficult time digesting because their gut bacteria is not well equipped to handle the task.
People who have lost their ability to drink milk or eat ice cream or other milk based products are called lactose intolerant. They are typically are not allergic to milk, although there are some who can be. Basically everyone starts out with the ability to digest milk. But if you cut milk completely out of your diet, after a few years you won't have the ability to do a good job of digesting milk products any more. That is because the bacteria needed to digest milk eventually dies out.
Milk products can then be gradually reintroduced to your diet, but it takes longer to be able to tolerate it again these days after you have eliminated it from your diet because most milk is pasteurized so that there is very little good or bad bacteria in it. It is the some of the good bacteria found in unpasteurized milk that help you to digest it. These days people who have problems digesting milk can buy a “probiotic” product that will help them. The probiotics are cultured bacteria that help to reestablish good digestion of sugars found in milk in this example. (There is also a difference between milk for cows and milk from other species including our own mothers.)
My wife has a serious food allergy to seafood... it makes her swell up and stop breathing. It is like kids who have an allergic reaction to peanuts. But vast majority of those claiming to have allergies to various foods don't have any type of true allergic reaction at all. Most haven't even visited a quack allergist of which their are legions these days, they just make this stuff up as they go along.
The most entertaining subset we know are all the people claiming to be allergic to gluten. There is a very small group that actually have been diagnosed with celiac disease which is a very serious autoimmune disorder, but in our experience the vast majority of those on gluten free diets are hangars-on who have never been diagnosed by an actual doctor. But if you go long enough without eating any gluten there is a good chance that you will eventually lose your ability to digest it.
The primary reason people have difficulty eating many foods is because of a lack of variety in their diet. The good bacteria in our guts that is responsible for good digestion is not well supported by the typical narrow diet of processed foods that people eat these days. And the processing of foods also kills off many of the good bacteria that we would normally be getting from the foods we eat. This is not completely a bad thing because those bacteria also cause food to spoil early in many cases. But it all contributes to people who lack the ability to digest foods as well as our ancestors.