I'm a multiplyer. I set up my PC, my gf's PC, my parents' PC, my steppatrnts PCs... whatever I do will affect a number of people.
Many PCs are configured by multiplyers like me. We pushed the use of firefox over that of IE in Germany. And we implement adblockers.
Now, why do we do that? It's not because we were asked for it. The people whom we help don't know that ads can be blocked before we tell them. No, we want to have less work.
How do we minimise our workload for administration of relatives' PCs? We secure them. Part of securing a PC is to make sure that only intended content is executed on it. That's why we install adblockers on so many PCs.
One or two years ago, a web-advertising company called "Falk AG" in germany got hacked. They had their banners on all sorts of resprctable sites like major newspapers. Suddenly, when you were visiting the websites of the leading German magazines, your PC would be hacked through manipulated ads served by Falk.
Again, we want to reduce the time we have to spend on those machines, therefore we want to keep them as clean as possible, therefore we make them block ads. What type of ad? Flash, animated gif, static image? I don't care. If it's not loaded into the browser, it cannot exploit a weakness.
Now for google.
If something needs to be found, it will be searched for, most likely using google. If all other ads are blocked, only the text-ads served by google on the google result-page will ever be seen. It increases their value.
Why would google care about banners on other people's sites?
And even if Chrome would not allow adblocking, what if a user actually found something in an ad he likes? He wouldn't have to google it. Google loses.
So, I'm actually surprised it's not google themselves who provide an adblocker for Chrome.