The reason why Servo has existed (when it was still in Mozilla's care) was because on how deeply spagettified Gecko's code (sans IonMonkey) was, with the plan of replacing Gecko's components with Servo's.
Firefox's automation systems are now miles better but that's literally the combination of years of work to modularize Gecko, the partial replacement of Gecko's parts with Servo's (like Stylo: https://hacks.mozilla.org/2017/08/inside-a-super-fast-css-en...), and actively building the APIs despite the still-spagettified mess.
V8 was dramatically better than Firefox at the time. AFAIK, it was the first JS engine to take the approach of compiling repetitive JS to native assembly.
If it's true that V8 was used internally for Google's scraper before they even thought about Chrome, then it makes obvious sense why not. The other factor is the bureaucracy and difficulty of getting an open source project to refactor their entire code base around your own personal engine. Google had the money and resources to pay the best in the business to work on Chrome.
"Why develop in-house software for the core application of the biggest company in the world at the time, worth more than 100B$. Why not just repurpose rinky dink open source browser as some kind of parser, bank our 100B$ business on some volunteers and a 501c3 NFP, that will play out well in a shareholder meeting and in trials when they ask us how we safeguard our software."
It's not quite that simple. I think that having that skillset and knowledge in house already probably led to it being feasible, but that's not why they did it. They created Chrome because it was in their best interests for rich web applications to run well.
