Probably because they don't see an important business case for it. Like everyone else, Google has limited resources and an enormous laundry list of business priorities around Chrome that involve all sorts of functionality besides IPFS. These include device compatibility, media capabilities, updates to the various HTML/CSS specifications, JavaScript and other automation functionality, etc. Then there's the never-ending list of bugs to be fixed.
You can, of course, try your hand at adding it yourself, or persuade others to add it - the core (Chromium) is open-source, after all. You can also try to assemble a critical mass of customers to persuade Google to add it.
(I'm sure you didn't mean it that way, but this post comes off as somewhat entitled, as though Google is your personal engineering team.)