My theory about cookbooks: They are not designed for cooking or even cooks.
Instead, the books are fantasy, to let the reader imagine that they could, will, might cook delicious meals and get praise, affection, love, and approval from their family, friends, and dinner guests. And for the onions, part of the fantasy is how easy the cooking will be -- brown the onions in at most 10 minutes.
It might be true of the more stylistic chefs out there for sure -- but I'll pull an America's Test Kitchen recipe rather than a random blog that shows up in google.
A good cookbook can be life changing, a bad cookbook can be near worthless (maybe this is true of any type of book). "12 Recipes" is a book a chef wrote for one of his kids to learn to cook and I loved it. Some soft cooking skills or other background information about what was actually important and what can be skipped really helped me learn to cook much better for myself.
I think the problem with some cookbooks is that cooking is a somewhat technical or scientific process. If the author is too technical, they can gloss over details that will trouble a home cook, like how tos for complex techniques that they are familiar with, how long things will take someone with less practice, how much prep / cleanup can add up at home compared with working at scale in a restaurant with dedicated prep cooks and dishwashers, etc. My partner was a professional chef for a catering company and the "recipes" they used internally had almost zero details besides ingredient ratios. I couldn't imagine trying to follow one without asking a ton of questions.
On the other hand, some people aren't technical enough and so they can't properly assess the details or break things down into a strong formula for someone else to replicate. They can be vague about measurements, timing, or technique, so even if you follow what's written your result is pretty far from whatever they had done in their own kitchen.
Then there are the "telephone" recipes that have been stolen back and forth from different blogs or articles without anyone making them and over time they've degraded into something just plain wrong.
Instead, the books are fantasy, to let the reader imagine that they could, will, might cook delicious meals and get praise, affection, love, and approval from their family, friends, and dinner guests. And for the onions, part of the fantasy is how easy the cooking will be -- brown the onions in at most 10 minutes.