Because the seemingly great choice of Webbrowsers in reality boils down to a risky monoculture of chromium (/its webengine). The only real alternative is Firefox/Blink. Risky, because the main driver behind Chrome-/ium (Google) is not acting on behalf of the public interest towards a free, open and privacy preserving internet. Instead they're working on a privacy exploiting one that gets locked down using DRM technologies. Them being a vendor of major parts of the internet as well as the browser to use it makes this a lethal combination. Firefox will definitely exist for as long as Google exists, because its their tool to defy claims of a monopoly, but they will do everything to keep it the small and mostly irrelevant "competitor" it is currently. Therefore, stand against Googles evil play and help Mozilla to gain some actual indipendence and leverage for keeping the internet free (as in freedom), open and privacy preserving.

There is a vocal contingent of people online who hate that chromium has the vast majority of market share of browser rendering engines.