Why RStudio is not picking up environment variables defined in $HOME/.bashrc

I use Arch Linux. I use SSDM as display manager, but I have disabled it with:

sudo systemctl disable sddm

I have put code in /etc/profile, $HOME/.bash_profile and $HOME/.bashrc to echo when those files are sourced. My $HOME/.bash_profile is sourcing $HOME/.bashrc (it came like that, I just added the code to echo when this happens):

if [[ -f ~/.bashrc ]]; then
	echo "$HOME/.bash_profile is sourcing $HOME/.bashrc"
	. ~/.bashrc
fi

I am exporting the following variable in my $HOME/.bashrc:

export R_LIBS_USER='MY_VALUE'

---- I boot my PC. It shows a prompt (in a TUI/command line) that asks for username and then password. I put them in and press enter. /etc/profile is source. $HOME/.bash_profile is source. The latter sources $HOME/.bashrc. This means that R_LIBS_USER is being exported. I'm redirected to a prompt. I do:

sudo systemctl start ssdm

Since SSDM is a child of that shell, it should inherit R_LIBS_USER. SSDM opens and I start a Wayland KDE session. Since this session is a child of SSDM, it should inherit R_LIBS_USER. I open RStudio from KDE. But R_LIBS_USER is still at the default value, not the one I have defined in $HOME/.bashrc. I show the value of the variable in R with:

Sys.getenv("R_LIBS_USER")

Where is my reasoning failing?