I suspect the list of people who switched to Chrome from Firefox, especially within the last decade, is vanishingly small.
In the early days of Chrome, it was svelt and lightweight compared to Opera or Firefox, but IE had the vast, vast, vast market share. Chrome handled tabs in a really cool way (the way ALL browsers now do it, putting them right in the application title bar in place of menus). The light touch and nice tabs made it worthwhile to switch at the time. And frankly, Blink was better than Gecko. But even then, the goal of all of the browser wars was to get people off of IE. IE didn't respect web standards and made it flat-out hard to build websites. Switching someone to Chrome from IE was super easy so many people were encouraged to do so.
For most of its life, people were switching from IE (and Safari) to Chrome. Not Firefox to Chrome.
Nowadays, Chrome is just everywhere. People know it, and it still has a fairly-undeserved reputation as being better than the default browser (Edge/Safari).
So the reason this feels so illogical to you is because that scenario just... wasn't happening.