Canceled Flight Rebooking Options via Amex GBT

When I book personal flights (through AA) and a flight gets cancelled, I can rebook via the app/chat/phone — almost always for no fare difference. In some cases, I’ve also gotten them to rebook me for no charge on a different non-one world carrier

However, when I book for work via Concur / Amex GBT, I can’t rebook with AA directly and my travel desk ‘issues’ a new ticket often with a fare difference.

Is that just how business travel with my company works? Curious if others have to deal with this.

With the snow storm on the east coast this week, my flight two days later to LHR was canceled — any my only option was to pay a $4k fare difference to book another AA flight.