afaik, Raspberry Pis move around 7M units annually.

Based on their first announced product (https://www.arduino.cc/product-uno-q), I think Qualcomm is trying to get into that space, and they bought Arduino for the brand name.

You're right that Qualcomm isn't in the business of small business. But maybe they expect that the market is big enough that it's worth their while to pay a subsidiary (Arduino) to do it.