During the social media ad pause of the 2020, we had multiple companies admit in earnings calls and elsewhere that pausing advertisement had no impact on their sales at all.

The extreme end of that spectrum is Tesla with no advertising whatsoever.

This kind of observation makes me pause and cause some reflection on ads in general.

Nit: Tesla has word of mouth advertising, which works for automobiles when you have brand loyalty.

Do they pay for it?

Well they have to pay some engineers occasionally to work on flamethrowers.

Yes - https://www.tesla.com/support/refer-and-earn

But that also means they’d be cheaper.

Advertisers don’t buy ads unless they have measurable ROI. It doesn’t matter if it’s 1000 impressions for $1 for 1 conversion, or 10 video views for $1 for 1 conversion, or a million impressions for $1 for 1 conversion. It’s just money spent vs money gained.

Marketers should spend every extra dollar on the ad platform with the lowest customer acquisition cost, so if Google ads are more ineffective compared to others, then its customer will go somewhere else and hence it will have less revenue.

Even at hypothetical 100% effectiveness, you're still going to be spending the same budget to match variable ROI on CPCs and CPA.