Alternate motivation: People stay engaged on the web more when pages are faster. One thing that makes pages faster is a faster browser. When people stay engaged on the web more, Google makes more money. Chrome's initial big selling point was being faster.
The core motivation wasn't speed -- it was ads. Chrome was designed to send people to Google Search instead of websites. The address bar auto-completion in Firefox would always suggest actual URLs, but Chrome's would send people to Google Search to click on ads on the way to their desired destinations. The ads started to become camouflaged so that most users couldn't tell them from organic results, and Google continued to make the ads harder to distinguish over time. I'm sure that Google also had long-term worries about ad-blocking and wanted to control the browser.
"We just want to make the Web faster" is what they tell their employees so that otherwise ethical people will write code that does unethical things. (AMP/portals is another example.)
As pointed out by another reply to your comment, Chrome was about pulling the users into googles ecoststem. By combining search bar with address bar, it blurred the line between a google search and a web address.
Just like Facebook, with its free basics internet deals with mobile providers in emerging markets, sought to confuse people into thinking Facebook is the internet, Google also sought to confuse people to think Google is the internet.
The investment in speed and other user benefits was a loss-leader for the goal of increased control. The speed and other benefits were indeed a net positive for users (and motivated Mozilla to focus on performance in Firefox) but they were investment made for payoff.
You've said it yourself: "the big selling point was being faster."
And yes, there is obviously some marginal value for Google in simply making web experience as fast as possible because it keeps people using the web. But that extended web use is of no good to them if users are doing so at non-Google properties that don't see Google ads, so it seems implausible that control was not a key motivator.
> That extended web use is of no good to them if users are doing so at non-Google properties
Extended web use is often punctuated by google searches, even if a lot of the engagement happens on non-Google properties. If slowness causes people to get bored and go do something else, Google suffers.
Disclaimer: ex-googler.