This is intended by default, for performance, we only populate the role relation. You can use the plugin extensions to modify the users-permissions plugin to adjust the population.
See the following code, you just need to add your 'user-groups' field to the array like ['role', 'user_groups']
The plugin extensions troubleshooting link I mentioned explains that we use a similar system to react ejections. Those functions are by default in the node_modules so you must create the file/folder path yourself and mirror the file contents to make changes.
Keep in mind that by doing so, you will need to keep that file up to date manually for every version update major or minor.