If advertising is no longer financially rewarding, is there not an argument that labor could transition into a different sector of the economy?

Companies based around advertising would die, yes, but they only exist in the first place because of how lucrative the activity is. Nobody is sitting around dreaming of how they could sell ads better than anyone else while not thinking of the financial compensation. At least I hope they aren't.

If someone was saying "many people have jobs in running offshore internet sports betting companies, if we put regulations on offshore internet sports betting, it would remove jobs" wouldn't the natural question be whether those industries are actually productive to have people employed in, or if it's a harmful industry overall? Generally in my view its somewhat sad that the system as a whole optimizes for advertising work rather than orienting in a way that everyone could be putting their work towards something they see as more fulfilling.

There is certainly more need for product discoverability broadly than something like online gambling, but I think the more relevant conversation is if the current advertising model is more like a local minima preventing progress towards a more economically viable method of handling product discoverability.