Some SEO guy once told me companies decide to buy these ads because it costs essentially nothing (b/c CTR is almost 100%) and improves the advertisers quality score.
This is the correct answer. Metrics that determine cost for these specific ads are so high, that the cpc is very low. This also ensures competitors don't buy it out, but also allows a company to slightly alter the consumer's journey (by choosing the messaging in the ad).
Yep. It's trivially easy to buy on your own branded keywords (your relevancy is unmatched) and very cheap. Sure, you'll cannibalize some of your organic traffic, but the risk of a competitor advertising on your keywords is too great
Ah, thanks, I didn't know price was inversely proportional to CTR.