For a good chunk of businesses, ROI tracking is really not that hard. It gets harder as your business becomes larger, or oriented more towards B2B, or in specialized niches, or online only businesses. I know first hand small/medium businesses (whom I've helped myself in the past) that basically survive on traffic coming from ads.

Obviously it all depends*. But I just wanted to chime in that it's not all totally useless, and "nobody clicks on ads". Us (tech-adjacent people), are less likely to be prone to it, but still get swindled through other sort of ads as well. It works more effectively for people not in our group. And keep in mind, we're in extreme tiny minority.