Using what everyone and their dog is using is prone to bugs just as much because software without bugs doesn't exist or is not very useful, but it also has the benefit of many versatile eyeballs looking at it in many different contexts.

So if there's a bug found and fixed in libxml2 which is used by almost everything else, everyone else instantly benefits. Same with libicu which is being used, for example, by NodeJS with its huge deployments footprint. Oh, and every freakin' Webkit-based browser out there.

OTOH, they rolled their own, so all bugs they hit are confined only to zoom, and are only guaranteed to get Zoom all the bad press.

Choose your poison carefully.