The core of IBM's business in the late 1970s was mainframes for large businesses. Should they have stayed focused on that, and not on the consumer PC market, or services today?
Their core market today is still mainframes for large businesses.
Their original business was typewriters and tabulating equipment. They should have stuck with that :)
The typewriter business was an acquisition! (Electromatic was the name of the previously independent typewriter company.) Time clocks and scales were the other original lines besides tabulating.