Does anyone know the reason for Alpine Linux choosing
Is it more secure, smaller in size or both? Or is it inherited from busybox?
I assume bash is the more widely known interface.
/bin/sh is a symlink to busybox ash.
The reason why busybox has been choosed is explained here
"Alpine Linux is a security-oriented, lightweight Linux distribution based on musl libc and Busybox."
It's a design choice. Alpine has been designed to be minimalist and to run in embedded system. Also with less (and smaller in size) software, the attack surface is minimal. If this sounds new, it is not, because this was the original goal of Alpine.
In this case, internet machine archive can help.
The main page at that time explained:
"Alpine is a modular embedded linux distribution for use in small appliances such as routers, VPN gateways, and more. The name "Alpine" stands for A Linux Powered Integrated Network Engine."
So, the simple answer to your question is: it's by-design.
Hope this helps.