I still remember the often-heated discussions in my former volunteer departments about whether, when and how members should, or should not, respond directly to incident scenes in their privately owned vehicles versus driving to their assigned station and responding on fire apparatus.
As I recall, we instituted similar policies that required all but chief officers, and some company officers, to respond to their stations and ensure the dispatched response vehicles got out, preferably with full crews. We did allow that a member who literally had to drive past an incident scene to get to their station could stop and render aid if there was nobody else on scene. But subsequent members were required to continue on to the station.
The rationale for such policies still strikes me as fairly simple. First, in most departments I know, the response units are what's dispatched, not individual members (except chief officers assigned to incident command roles, in many cases). Second, there's only so much a single firefighter, or even a group of firefighters, can do without the appropriate complement of apparatus and equipment. Third, what would happen if everybody went directly to the scene instead of the station?
There's no question that volunteers, and sometimes career firefighters going to/from their work locations, occasionally face a dilemma when called to, or arriving upon, a fire or other emergency in their POVs. Stop immediately and do what you can to help without the proper apparatus, tools, equipment, and PPE. Or drive to the nearest fire station and make sure that all the required vehicles (and firefighters) are able to respond to the call.
Like so many decisions in the fire and emergency services, it's hard to anticipate every possible situation that might arise, and the "right answer" for a given incident will probably depend on how each department's members are deployed, equipped and trained.