It is about the integrated experience. Most big companies I know of actually hire recruiting co-ordinators for scheduling and following up with potential candidates as well as with interviewers internally. If Google can use their G-Suite products including Gmail, Calendar, Docs etc. to provide a seamless recruiting experience, I would give it a shot - especially if my company is already on G Suite.

Now that Google has the building blocks for businesses - Gmail, Docs, Calendar, Video Conferencing etc. - it makes sense for them to get into common enterprise services. This ways they can extract more rent and also provide an integrated/more valuable experience to their customers.