At least currently the single subaccount view is deliberate, meaning that viewing more than one subaccount at the same time in the ATOM service app is not possible.

In case of very large fleets the vehicle map gets overcrowded with vehicles and the operators can be overwhelmed as a result and not have a clear view of the vehicles they need to manage on site.

In cases when subaccounts represent different cities where you operate the single subaccount selection makes more sense - only the vehicles in the relevant city are shown to the operator.

Additionally, showing only the relevant information instead of all the vehicles improves app performance / loading time.