You are so Naive dude...you have no ideas the kind of knowledge/skill transfer, the exposure, let alone establishing Nairobi to a tech hub in Africa, you're just looking at direct jobs...makes me question your level of education..
The kind of transformative products and services which will be developed will have a huge impact to the people in general.
It will also provide a platform for Researchers which could lead to lot's of start-ups coming up (how'd you think M-pesa came to be)
It's a dream come true for visionary engineers, product managers, UX, UI designers and learners-now that coding is in the syllabus,you dont have to fly to California for benchmarking.
Not to mention easy access to fast and cheap internet services...
Such developments from multinationals have a huge ripple effects in developed countries,let alone middle income/developing countries. There would be a huge impact if google opened a tech hub in say another US state... Did you see what happened when they moved Boeing from Seattle to Chicago?
And you here comparing a whole Google tech hub to a mining expedition which only provides you with food for today...