> Prototyping platforms have tiny markets, but lead to downstream sales. Many a company were brought down by more developer-friendly platforms ignoring the "tiny" userbase of people who want to do unconventional things.

Qualcomm doesn't even make small/cheap MCUs so they aren't going to win over that market by buying Arduino. Their first board post-acquisition is a mashup of a Linux SBC with an MCU devkit, and while the Linux SOC is from QCOM, the MCU is from ST Micro.