The filesystem hierarchy standard says that each add-on package under /opt should live in its own top-level subdirectory (e.g. /opt/<vendor-or-pkg-name>). By creating a shared /opt/python-venv namespace for many venvs, we're effectively putting multiple products under one tree.
There are also differences between RHEL and Debian (especially Debian 12) on where to put Python venvs the right way.