Because in real life it doesn't take that many people making purchases and other transactions to reach 5000 t/s. I do as many as 30 per day easily.

5000 t/s makes up 432 million/day. It would only take some 14.4 million people (with a usage pattern similar to mine) evenly distributed across the world to reach that limit. (Much fewer people if they are in the same time zone or close).

Bitcoin must scale to more than 10 million odd people.