It used to be you could just "clear your cookies" and you'd have a virtually clean identity on the internet. Now basically every ad platform, including Google Ads, is heavily encouraging the use of "first party data" - aka name, email addresses, phone numbers, mailing addresses - as a way to target customers. Google Ads help docs specifically cite the phasing out of cookies as the reason advertisers should send Google as much "first party data" as possible.
In effect, that means "clearing your cookies" will do nothing if you're the average Google users who's still logged into chrome/google after clearing your cookies.
And instead of Google + ad networks just having your data in cookies, now they have your name, email, mailing address, zip code, etc provided to them on the backend with no way for the consumer to easily opt out or delete their data.
Edit: adding another supporting example: for advertisers tracking conversions, it’s no longer good enough to just fire a conversion pixel on a checkout page. Now it’s heavily encouraged to send the user’s personal data (email, name, phone, etc) along with the conversion pixel/tag so Google (or whatever ad platform) can match the conversion to clicks without cookies at all. This type of conversion tracking was not pushed or encouraged until browsers started phasing out 3rd party cookies.
Edit 2: Google has even gone as far as adding a setting to their AdWords tracking tag that automatically scrapes the HTML of a page in search of anything that resembles a user’s email address or phone number to make it easier to collect first party data automatically.