Plus, it's extremely tedious to collate and filter all of the properties needed to make them work. Ebay and Amazon barely do it at all. Newegg and McMaster Carr do OK. Only EE components seem to be demonstrate the ideal parametric filter systems that negate the need for advertising.
But I'm still a sucker for buying Linear Tech or TI components before, say, Maxim or Toshiba because even if the parametric search say that both options fit my requirements, the former seem to be better documented and more user-friendly than the latter. That's the kind of advertising you only get through years of writing expensive and high-quality technical papers and producing high-quality parts, and I suppose there will always be value in advertising that fact (or suggesting that fact, regardless of whether it's true for other advertisers) to less experienced engineers.
Hah, reducing your BOM cost isn't a major factor in your decision making? ;)
for example, for microcontrollers:
https://www.digikey.com/products/en/integrated-circuits-ics/...
I wish we had that in more fields. Would provide huge value, but it's a hard problem. But i suppose if with the right incentives(banning advertising ?), we could do it.
The other source of info for EE's is education and PR, some of it probably pretty unbiased(at distributors sites), due to incentives.
As for ads ? they exist, but they seem to play a relatively small role, and probably nothing major will change if they stopped existing.