You're painting a rather bleak picture -- that the majority of creators/influencers' content is advertising. If that's the case, I'm not sure why Youtube/Instagram should also tolerate that -- it's basically spam on their platform they haven't curated through their ad network.
I’m not sure why you would presume that. Also, product placement has been a standard feature of entertainment for a long time. I don’t see why you’d expect Google and Facebook to be the ones to take a stand on this, after all this time.
Spam is something the recipient doesn't want. What is or isn't spam is subjectively determined by each individual recipient. If spam were strictly determined by what nobody wants, requiring complete consensus, then nothing would be spam because in a world of 7 billion people there will always be one nut who welcomes the unrequested solicitation.
Creators are very careful not to overwhelm their audience with ads; their audience (and their portability to new platforms/ channels) is their number one asset since they may need to jump to new platforms in the future as their channels can get demonetized/ banned for frivolous reasons.
[0] https://influencermarketinghub.com/creator-earnings-benchmar...
Except if they believe you are not advertisement friendly content.
Like any discussion or educational material about any touchy topic gets not ads (and there are a lot of such thinks).
YT accidentally mistaking a think you sayd as a black listed swear word (even if you didn't say it and are not even speaking in the language its from and it just sound similar) => No Ad Money.
Politics => No Ad Money.
Covering Covid related thinks => No Ad Money.
Covering local news including violence => No Ad Money.
etc...
Advertising embedded in the content as sponsor callouts and similar (often paying way better then YT ad sense), this includes showcases of sponsored content and similar.
Which if it's properly labeled is not a problem.
But as far as I know many big YT channels can NOT live from YT ad sense/network money. Some won't even get any at all due to YouTubes (IMHO overreaching) classification of content into advertisement friendly or not.
For example, a guy is teaching me to fix a generic, unbranded toilet issue but stops to mention a particular widget or toolbelt he is being paid to use.
Next video he is teaching me to fix a sump pump and there again he mentions his sponsored plumbing gear.
This is fine by me. I learn how to fix things and some plumbing widget company pays the bill.
If the platforms wanted to come after the money, they could. I suspect they're still in the growing phase. But I imagine in the near future, they'll start demanding all ads go through their platforms.
The fact that you call them "Youtubers", identifying them using the trademark of one particular platform rather than a generic descriptor like "video content creator", suggests that there is not quite as much healthy competition as you claim. Most video companies other than youtube only compete with youtube in a narrow sense; a great deal of the content on youtube does not fit on tiktok's platform, which is only good for short-form content. Netflix only hosts movies or TV shows. Twitch is for livestreaming; other kinds of content don't fit into the paradigm of twitch. Vimeo has never been a good place for off-the-cuff home movies, they too try to compete with youtube only in a narrow domain, not across the board. The few generalist video hosting companies other than youtube are all jokes that are faaar behind youtube in viewer counts.
TikTok has a fund to pay people to make content to get them up off the ground.
Insta, despite it's growth, has a decay problem in that it's out of the zeitgeist of the key demos. it's growing in developing markets and maybe might have some incidental sign ups, but people are not flocking to it.
And TikTok - depsite it's popularity, has a very 'fad' feel to it. While FB has a bit of the 'e-mail' incumbency in that it's how people communicate with family and user groups, TikTok is a bit more fleeting.
These platforms would get hurt badly without a lot of those middle and upper tier content makers.
The current situation is a rational entente actually: Insta makes ads, influencers can make a buck however. The more popular YouTubers will monetize with ads anyhow.