ADVANCED COMMA EXPLICATIONS: Please help me

This posting is about exclusions of the comma where I would otherwise feel inclined to include one. I've presented various excerpts from sentences in which I've encountered whilst reading an actual English grammar text.

Stately, I have been thoroughly researching the so called rules of correct punctuation; therefore, I am politely requesting detailed examples for comparison between sentences where a comma would be included as opposed to similar sentences where a comma would otherwise be excluded.
Merely quoting the basic comma rules will not resolve my dilemma.

1. NO COMMA AFTER THE ADVERB (USUALLY) AS AN INTRODUCTORY PHRASE? Example from an excerpt taken from an English grammar book:
"Usually when adjective phrases modify nouns, they are attributive..."
Why isn't there a comma following the adverb usually in the above sentence? Please provide me with examples of related sentences for comparison. I need to know why this is. No comma after "usually" as an introductory phrase? What?! Why?! I feel inclined to begin such a sentence like this: USUALLY + COMMA... Please provide me examples of sentences where the comma is utilized VS. examples where it is not.

2. Why is there a comma after "sometimes" in the following sentence?
"My husband does the cooking, sometimes." This makes absolutely no sense to me, as this excerpt was taken from an English grammar text. Personally, I would never dream of INCLUDING a comma preceding the word sometimes in that sentence.

3. No comma after "in fact" or "for example?" I've observed numerous sentences where "in fact" and "for example" begin a sentence and there is NO COMMA following that phrase. This makes absolutely no sense to me and seems contradictory when considering the rules of basic punctuation.
Thus, I was taught to always include a comma when beginning a sentence with a phrase such as (for example, <---), and or (in fact, <--)!

An excerpt from a grammar book: "In fact we want them to be critical readers, ..." Whys isn't there a comma after the phrase "In fact" Why?!

4. No comma after a prepositional phrase that is presented as an introduction to a sentence?! This is frustrating!
An example of an excerpt from an English grammar book:
"On the day after that she was involved with several tasks-- Why isn't there a comma after THAT? On the day after that, <--- why no comma?!

5. Excerpt: "On the next day she did not appear to be very tired at all--" The word day is a noun, followed by the subjective pronoun "she." Supposedly, we are supposed to separate nouns with a comma. Shouldn't the above sentence be written like, "On the next day, <--- (COMMA), she was involved in...

6. No comma after THEN as an introductory word?! What?!
Excerpt: "Then for three dreadful days she did not appear at all." ------------ Why isn't there a comma placed immediately after the word THEN? Such as: "Then, for three dreadful days?!"

7. Excerpt: "In making my choices I have concentrated on those who-"
Why isn't there is a comma separating "In making my choices" from "I have concentrated on those who..." ?!

8. "From all this you will gather that I believe....blah, blah, blah-"
Why is there no comma immediately following the introductory prepositional phrase "From all this..." ?! Shouldn't there be a comma separating the phrase "from all this" ---> from "you will gather that I believe..." ?! Please grammatically analyze this sentence structure in such a way that I can comprehend the justification for such punctuation.

9. "In selecting the entries I have kept in mind the great amount of subject knowledge teachers need." ...Again, why isn't there a comma separating the phrase "In selecting the entries" ...from "I have kept in the great..."
As in, "In selecting the entries," <--- COMMA, "I have kept in mind the great amount of subject knowledge teachers need."

ALL OF THE EXCERPTS PROVIDED WERE EXTRACTED FROM A CAMBRIDGE ENGLISH GRAMMAR PDF.

Please help me by submitting detailed answers. Similar sentences as comparative examples would greatly assist my understanding, not merely just quotes from English texts concerning punctuation rules. I have amassed many English grammar manuals and have therefore studied the so called comma rules quite thoroughly; yet I am still VERY confused.

No one has ever taken the time to teach me; as I lived an exceedingly unstable life growing up.

The comma rules seem to be exceedingly contradictory. If only someone would invest the concern and time then I could move forward.

PLEASE HELP; AND SPARE ME ANY INSOLENTLY CONDESCENDING REMARKS OR APATHETIC RIDICULES.

Thanks,
some guy