Earlier quoted context omitted.
Because it can't be extended so much as the r-pi. Why limit yourself when you don't have to? It's like asking why one would buy a 1TB harddrive when Linux fits in a few GB.
>Why limit yourself when you don't have to? Cost, power consumption, reliability, performance, security, weight, and volume, to name just a few. I really dislike the attitude that we should use the biggest hammer we can find for any size of nail just because we can.
> security
The ESP8266 is a product developed by a Chinese company, which would be reason for some to avoid it from a security standpoint.