It seems like the blog is referencing the documents posted directly on Netflix's website[1], the early versions of which do open up with well-designed cover pages.
In contrast, the link you shared is perhaps the direct filings that the SEC receives from the company, which may remove these designed elements prior to filing.
That's what I figured. So the blog post is completely off-course - this person is complaining that the Investor Relations site no long has tarted up versions of the annual filings.
"One fine day, as I was following the internet rathole, I landed myself on the Netflix investor page for some reason. One thing to understand about these 10-K forms is that these are …. pretty basic."
Like the vast majority of companies that just need to comply with their regulatory requirements.
Although the author may be wrong about whether the 10-Ks he saw were the same ones being submitted to the government, I think his curiosity is still worth indulging.
Why did Netflix slowly stop designing their 10-K reports that lived on their own investor relation page?
My own guess is that there was some downward pressure to just produce the basic report, since that's all the government would see and investors wouldn't really value the design.
If I had to guess (other than the general comings and goings of style), it would have been related to the increasing (mandated) usage of XBRL. The visual presentation was no longer as interesting as soon as you could extract the data in a machine readable format.
Except joke is on them because XBRL and the GAAP taxonomies allows "extension concepts" or tags(1) which basically means "we can make up our own reporting identifiers and you can't do anything about it" and makes categorizing accounting data very difficult across companies.
In contrast, the link you shared is perhaps the direct filings that the SEC receives from the company, which may remove these designed elements prior to filing.
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[1] https://ir.netflix.net/financials/annual-reports-and-proxies...