Toshiba to invest $1 billion in Southeast Asia over next 5 years

Well that is vague. Anything more specific? Such as, where, and for what?

Why not invest in Japan more?

at least in the automotive industry (not sure about electronics) parts come from Japan iself and much of Japan's "foreign factories" are just assembly plants.

The Japanese companies are excluding China and Japan for the investments because most of these investments are for the infrastructure.