.bash_profile not sourced when running su

Using su without -l or - starts bash as an interactive, but non-login shell, which doesn't read from either of the files you specified. Use the -l or - option or put the relevant config into /root/.bashrc.

Quick summary of config files:

• Login shell (-l/--login) reads /etc/profile first, and then the first it finds of: ~/.bash_profile, ~/.bash_login, and ~/.profile.
• Interactive but non-login shell (-i) reads /etc/bash.bashrc and ~/.bashrc, in that order (unless the --rcfile option is used and tells it to look elsewhere).
• Non-interactive shells, e.g. started from within another program without using the -l or -i flags, reads the file specified in the BASH_ENV environment variable.
• When run as sh as a login shell, it will read /etc/profile and ~/.profile, in that order.
• When run as sh as an interactive non-login, it reads the file specified in ENV.

Bash behaves differently depending on if it believes that it is a login shell, i.e. the first shell run when you log onto a system. It only reads .bash_profile if it is a login shell. If you put the PATH-changing code into .bashrc instead, it will be run for all interactive bash shells, not just login shells.