It's a lot easier than building a whole browser from scratch. I salute what Mozilla is doing but I still don't want to use their browser because it just isn't as good, in my opinion. (Firefox also does't support the MIDIAccess API yet, which I need)
Obviously a lot of people agree that Chrome is better. I'm a lot more likely to use Microsoft's Blink browser than I was to use Microsoft's fully proprietary browser, but even better would be a fully open source, community steered "UnGoogled Chrome".