Arduino you write bare metal firmware, raspPi you write software on a host OS
firmware does not have the overhead of a host OS. super low power modes, instant sleep/wake, exact control of instructions/clock, far fewer security issues.
Cheaper, more powerful, more feature-rich Arduinos, if you squint. I'm not sure why you would actually use an Arduino™ unless they've really improved their lineup since I last looked.
If you can get them for $2.50, then yeah that's competitive, but the official site lists the Arduino Nano at $20.70 and it appears to be weaker than the Teensy-LC at $11.65, or ESP 8266 series at <$5 for a 5-pack (why Amazon only seems to sell them in bundles is beyond me). And the Teensy has a better chip and can do USB mouse/kb emulation, and ESPs all do wifi. If you can get them for $2.50 and don't need more power or features then yeah that's a good pick, but I maintain that official Arduino™ boards are not an obvious first pick.
Oh, I definitely agree with you on that. Unless you're a school or similar institution that needs to go with the safe choice, I really don't understand how Arduino™ makes any sales.
The clones are so much less expensive than the official Arduinos that there's no comparison. Even the versions that Adafruit makes that IMHO, improve the design cost less than the official arduinos. So it's not a surprise that the Chinese clones will be dirt cheap. I'm not complaining though. I have a board where the Nano (clone) itself is by far the cheapest "chip" in the BOM. Precision analog devices are expensive and my 50 or so boards sold each year can't compete with the Shenzen manufacturers' economies of scale.
firmware does not have the overhead of a host OS. super low power modes, instant sleep/wake, exact control of instructions/clock, far fewer security issues.
Teensy and ESP32 are just souped up Arduinos.