Aren't you forgetting about the software that makes it so easy and straightforward for newcomers to flash programs and experiment the microcontroller?

First, the software is available whether you buy the board or not.

Second, there's no real difficulty barrier, not anymore. There are point-and-click tools, free integrated IDEs, cheap programming dongles, etc. There are more tutorials for Arduino than the underlying chip, and I'm not saying that doesn't matter - but it boils down to the community, not the hardware.