Other answers have already addressed the point that the Republican National Convention will nominate a candidate, but I'd like to address an additional point.
(...) why does Google only consider him the likely nominee?
(Emphasis mine).
Because Google is just a search engine. The results they provide merely reflect what others on the Internet are writing about it.
Not only does Google not have a say in who the RNC will nominate, they aren't a media outlet either. While some journalists / bloggers / pundits may draw that conclusion, Google's job is not to draw conclusions, just to report back what can be found about a subject on the Internet.