I once worked for a company that operated along these lines. It wasn't quite as bad as those mentioned in the article due to the fact that the industry in question had several government agencies watching almost everything they do but it was an interesting learning experience.
There's likely two reasons why so many follow the same pattern. It's possible that many did enough A/B testing to determine the best direction that provided the best results. More likely one person came up with the pattern, the rest decided that it seemed a successive effort, and they all copied that one person's pattern.
I can't tell you how many times I created a landing page and/or email that was built in one specific way that originated with one guy that the rest perceived as the most successive guy in their type of marketing. If he said it, then it was gold. It was a tad disheartening as there was no real design involved. "Copy is king!" was the mantra and a nice design was not necessary. Even a decent design that made the copy easier to read was not considered worth the time. This was typically the type of landing page that uses the funnel method of long, sensational text with call-to-actions sprinkled down the page leading to a short order form at the bottom.
This insistence of copying everybody else because of perceived success, no data to support that perception of course, made for interesting conversations. "We're doing it this way." "Why?" "Because that's how they did it." "Why should we do it because they did?" "If they're doing it then it must work."
Although it was always fun to introduce a new kink to the marketing pattern and watch everybody else copy you. Especially when we hadn't yet decided if the new method even worked or not.
My favorite story that shows how locked into a pattern they would be until something shattered their illusions involved one sales email. For the longest time it was the rule to use as few images as possible in emails. The reasoning being because modern email clients do not automatically download images so you don't want things hidden from the potential customer before they interact with the email. I fought that quite a bit using legit companies like Apple and NewEgg as examples in that they successfully sell stuff and use images quite frequently through their emails. No dice. So one day I design a new email template that did use images heavily, our products were displayed in a grid that looked like stickers placed on the email. That meant that the copy listing details and pricing of the products were in the images, which was a no-no. I didn't tell anyone I did this knowing that all of them had their email clients downloading images automatically that came from us. The email was approved and sent out. A few weeks later I asked how that email did, "Best money-making email we've ever sent out!"
I then confessed to what I had done to their totally shocked confusion. After that I was able to actually design stuff that looked nice instead of the scammy look they insisted upon. And of course most of those newer designs, not all mind you, made more money. Interesting that I didn't see many other companies copying the new pattern. I guess it broke the mold enough to not be perceived as successful.
Anyway, even with the occasional moral problems, it was a good learning experience. Almost everything I know about SEO, ads, email, marketing, analytics, customer relations, and much more came from this company. Kind of gives me a somewhat unique perspective at my new job at a more traditional agency.