For most hardware projects I reach for Arduino first. They are a lot cheaper (especially the knock-offs), actually in stock, and easier to reason about (fewer layers involved in the software stack, more direct hardware access)

Raspberry Pis are great if you want easy internet connectivity in your hardware project, or need an OS or lots of computing power.

If they were readily available and $20 each I'd grant them that they are more convenient. But at real prices and availability that's more difficult to justify