Why are some busybox commands in interactive mode not available in a chrooted environment?

I try to setup a most minimal chrooted environment using busybox.
I created a directory 'testRoot' and copied 'busybox' into it.

from this directory I execute:

sudo chroot ./ /busybox sh

now I have an interactive environment. commands like 'ls' and 'pwd' work:

BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.2) built-in shell (ash)
Enter 'help' for a list of built-in commands.
/ # ls
busybox  testje
/ # pwd
/
/ # 

some others (like 'vi') doesn't:

/ # vi
sh: vi: not found

on the otherhand starting vi outside the interactive shell works:

sudo chroot ./ /busybox vi

and outside the chrooted environment in the interactive shell there is also no problem:

eldendo@eldendo-WIM2140:~/testRoot$ busybox sh
BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.2) built-in shell (ash)
Enter 'help' for a list of built-in commands.
~/testRoot $ vi (--- vi starts up here ---)
~/testRoot $ 

Any idea's ?