Because what Google considers a good search result is not what users consdier a good search result.

Why is every search result for even the simplest yes/no question a 1500 word article with 2-3 picture and an embedded video? Because that's what Google thinks is a good search result!

Google penalises your search ranking if users quickly navigate away from your page - this means if you have a page that quickly an efficiently answers a searchers question you get penalised whilst the site that buries the answer two thirds of the way through pure blog spam gets rewarded.

What is the incentive for "fixing" anything? Removing 1 ad improves the search experience but decreases revenue. On the other hand, adding 1 ad increases revenue. At this stage that's all the innovation I see google doing.

Google services are paid for by advertisers. On the fair market, there is competition that forces prices to decrease. Google is forced to sell more ads at the same price, or competitors will displace it from the market.

"Fixing" search is, at this point, to Google, "getting people to click on more ads"

Because their revenue don't depend on search quality, they get paid for the top spots regardless of what's on the bottom and they are at a near monopoly.

Do they make more money if I click on a few SEO spam sites full of Adsense, and page through a few pages of Google results, before finding the answer or possibly giving up - or if I find and click on the top result?

Don’t worry, the brain drain is in progress.

They are all working on ads and adblocker arms race.