I've seen the exhaustive essay style on professional pages too. Some people enjoy creative nonfiction, both writing and reading it, along with connection between writer and reader. Some people want to cut to the chase. And that's a difference between conversation modes in general -- most often, women want to talk about their feelings and men want to figure out actions, but it varies.
There is, of course, another reason: more writing means more room to cram in extra ads. Mostly that just makes me close the site and move on to the next, but other people must tolerate it enough for this to become the norm. Honestly, if you want people to read what you write, let them see THAT and quit acting like a cat with your ass in their face while they're trying to read it.
Regarding instructions, I've read ... gosh, probably hundreds of cookbooks by now. Some of them are very good, and others are execrable. Modern ones routinely leave out ingredients, list ingredients but don't tell you what to do with them, gloss over how to do things, and almost never explain why to do things. Being a good cook doesn't mean being able to write, nor vice versa, but if you can both write and cook, you can easily beat most of what's on the market. :/ So I try to do better with mine.
When I post recipes, I'm rarely in it for the socializing. I may drop a few lines of context at the top, but then it's on to the recipe. For me, I put the chatty stuff at the end -- how I made this and why, variations I or you might try in the future, which ingredients are crucial and which can be freely substituted, what they even are if I've used something uncommon, and so forth.
I suppose it helps that I'm not actually trying to sell anything. I just like food.