Why would anyone need a reason? I mean it seriously. Chrome users on this platform really baffling for me. They know what the consequences are, they know quite well what the icon with their picture on the corner does. Still being OK with this is super interesting.
Most products are often get grilled here for having closed code parts or similar concerns but when it comes to giving complete audit of their online existence, "meh...". Same folks who criticize canonical (which I disagree strongly with their late practices) only to install chrome as their browser on their systems.
I think the big difference is stated purpose vs execution, especially combined with who/when that elicits a response vs passive agreement/disagreement. An extremely small proportion of even the super techno-nerd crowd are really about the principles of open source, all other considerations be damned, when selecting software to use. That said, when something claiming supposed to be the bastion for that use case and antithesis of what the closed for profits do does something they'd expect from the latter it elicits an extremely strong response from nearly all of those that are as well as a good portion of those who have other considerations just because of the hypocrisy. Windows/macOS adding a new Bing or Siri integration somewhere, while getting some mumblings, isn't going to illicit nearly the same kind of reaction from the crowd though as everyone already knows and expects that of them. The majority of even highly technical users tend to use software based on what they find most productive, not necessarily the software with the best policies and licensing. So, statistically speaking, you tend to get complaints about open source software not being up to snuff or principle followed by most people choosing non-open software much of the time anyways because they feel it works better for them.
For Firefox specifically, it's long failed at holding the web back from Chrome and the choice isn't about that anymore. That title has firmly been with Safari for a long time now. Because Safari isn't available on all platforms it leaves not much of a concern to choose a Chromium based browser outside that group who operate solely on principle not 100% of the browser is open source.
I think for a long time Firefox languished a bit too far behind Chromium in many architectural aspects (I remember waiting fooooreeever for Electrolysis then when it came out the browser was significantly slower than Chrom* at the time). This comparison is leaps and bounds better today but it's a bit of a day late, dollar short situation in that it's not better enough to get droves of people to switch over again like the IE vs Firefox era.
The other thing I'll mention is when the topic of browsers comes up people's goto is the last issue they personally had with each. Given the size and complexity of browsers combined with the amount of hardware, OS, and use case variance this tends to feel more akin to people arguing whether lottery numbers skew odd vs even based on their last experience than anything about the actual browsers. Even when the discussion steers towards talk of a specific feature a lot of the time that feature didn't even originate in the browser it's being brought up for.
Firefox stutters. Every couple of seconds, if I'm doing anything active on the page, it freezes up for a fraction of a second. I have no idea if that's a garbage collection issue or what, but it makes it painful to use.
That being said, I'm on Safari instead. Chrome doesn't make me happy.
Most products are often get grilled here for having closed code parts or similar concerns but when it comes to giving complete audit of their online existence, "meh...". Same folks who criticize canonical (which I disagree strongly with their late practices) only to install chrome as their browser on their systems.
Insert "statistically speaking" wherever needed.