Why Chrome, IE, Edge, Safari or any other browser?
To be blunt, most users aren't too discriminating about the browser they use, and just use the bundled default on the device or computer. The same could be said for email clients as well.
They don't know KHTML from WebKit, Blink, MSHTML, Trident, Presto, or Gecko, nor do they care.
Unless there is a desired feature, compatibility issue, or other problem to be addressed, they're unlikely to seek an alternative, and even then it may only be employed at certain times to solve a specific problem (like a bad online banking site), and not become their primary browser.
The browser ballot imposed by the EU's settlement with Microsoft in response to IE's dominance was designed to make users aware of other browsers available to Windows, and have them make a conscious choice. The way the winds are blowing, Apple is drifting toward that shore as well.
Every new browser touts that it will be the fastest, most compatible, or whatever, and initially, that is usually true. Chrome was fast and light, compared to its peers, but like others, it, too succumbed to getting slower and more resource hungry. Technology progresses, and without the will and commitment to devote resources to continuing development, stagnation occurs, and the situation becomes ripe for the competition.
As a rarity for Google's products, that often fail to stick to walls, Chrome is successful because it's a competitive product, is heavily promoted, and promises better integration with other popular Google products, as well as being the default on Google's devices. Safari enjoys similar benefits among Apple users.
Those who recall the days of the Windows, and by extension, IE hegemony will recognize why a dominant browser, or platform, is bad for users. As a Apple user in those days, sites that "worked best with IE," didn't function properly, or flat out rejected other non-IE browsers were not an uncommon thing. Even worse was that, like Windows, IE was a mediocre product, and gave MS undue influence over the web.
A similar situation existed with media, with QuickTIme, RealPlayer, Shockwave/Flash, and other proprietary standards battling and causing unwarranted headaches for users, forcing the installation of different extensions, and codec packages, just to simply make full use of the web, which was designed for open, agnostic standards. It was a mess that wasn't solved until HTML 5 media became the norm.
Make no mistake, these companies, including Apple, don't devote sizeable resources to developing browsers out of the goodness of their hearts, but for their own self-interest. There are some real competitive advantages, both technical and business, that are expected in return, and depending on one's viewpoint, that can be a good or bad thing.
The likelihood of compatibility issues as severe as in the past isn't as high, but it's still important to have players like Mozilla and others play a role, even if only to keep the giants from becoming lazy, complacent, and not striving to advance the technology in general.
The direction of the free and open web being driven by a single company, no matter if it's Google, Apple, or Microsoft, is not a good thing, and the notion of a benevolent Google Chrome, or Apple Safari, is a myth.