Oh, this one again.
Birmingham was fortunate to have a British Airways base for many years, who tried and tried to market their services and lost money, often bucketfuls of it, every single year. In the end they dropped them over to FlyBe, who have sort of bumped along the bottom with profitability, nothing spectacular.
Many of those they quote who go down to Heathrow are headed, a few at a time, for Cape Town, Minneapolis, Moscow, Cairo, etc, etc. Do we really believe they would all get direct services from Birmingham ? And as the airport has capacity, why haven't they been started ?
Why are there no Air France intercontinental services from Lyon (France's second city) ? Why are there no Lufthansa intercontinental services from Hamburg or Berlin (Germany's first and second cities) ? Because non-hub operations do not work financially. Get used to it.