The majority of people are not digitally literate enough to care about what they're using. How do people preserve social justice if they're not aware that it is being violated in the first place? Who would deliberately step sideways and do something that requires effort when they have no incentive to? Most people just do what is convenient, without bothering to think twice about it.
Google used a lot of its gigantic resources and ad spaces to advertise Chrome everywhere. It's been installed and enabled by default on most mobile devices for years. Google paid software publishers to have Chrome distributed through other software installs (it also bundled it with its own software like Picasa and Google Earth). It also paid my local (state-owned) public transport operator to display gigantic banners in my train station. It organized events in my work community to promote its software and services, including Chrome of course. For years, its search engine told me to install Chrome every time I access google.com from another browser. Google stills serves old and ugly results page when I do search from Firefox (e.g no chart shown when searching from Firefox, although every other financial websites is able to perfectly display their stock charts in non-Chrome browsers). They've even been fined billions(!) of EUR for illegal practices involving the distribution of Chrome)[0].
People may have made different decisions to chose their browser for good reasons, but Google also built a monopoly for very good reasons, too. Users were and are still constantly pushed and incentivized to use Chrome, because of extensive, multi-year PR campaign, digital and outdoor ads, but also technical tricks.
Which sadly includes me these days, since it's such a pain to run multiple versions of Firefox and there are legacy extensions I can't do without for some things.
I interpreted the comment to mean, they run old FF (with extensions) alongside chrome (incompatible), because they don't want to run two versions of FF. I don't quite understand this either, but it makes more sense than the other interpretation, I think.
Bingo. DownThemAll is something I would describe as "mission-critical". I had trouble getting two different versions of Firefox to not interfere with one another in odd ways such as everything running fine until I open a file with Firefox as the associated program and one version would open but have all the settings from the other version and Portable Firefox refusing to save settings or extensions at all. Using Chrome for casual browsing was just less of a headache.
>I had trouble getting two different versions of Firefox to not interfere with one another
This shouldn't be an issue if you run your secondary instance with -no-remote -profile="your separate profile".
>Using Chrome for casual browsing was just less of a headache.
That still doesn't answer the original question though. Why choose chrome over firefox, when it has no legacy firefox extensions? Does chrome have those legacy extensions' features built in? Was chrome better than firefox, and the only thing keeping you on was the legacy extensions?