It hasn't been technologically possible until recently, and now that it is, businesses are strongly incentivized to use it, in order to keep up with the growth of competitors that do used tracked advertising.

Privacy-focused mass-market products like DDG and Firefox will very rarely be able to keep up with the giants that prioritize profit. As long as users disregard their privacy, there'll be businesses ready to entice them with customized features, and of course advertisers will reward that too. That's why regulation is the only real way out (GDPR, etc.).