Rumours are that LPL have recently benefitted from PPE charters arriving there because handlers at BHX are currently refusing to accept bulk-loaded cargo charters.
Reasons that destination airports for cargo charters are chosen (no particular order):
Customer preference - often proximity to end user, ground transport considerations
Price - fuel burn to airport, airport charges, handling & freight charges
Aircraft specific - aircraft category for runway, taxiway and stand compatability
Availability of handling - agents and equipment, time to get cargo available
Timings - Airports, handling and even customs/transit shed availability
Airline preference - regular destination for them, contracts in place already, line maintenance hotac/crew swap considerations, ability to pick up return flight
The customer will not always have the final say on the destination - they maybe persuaded that another airport is preferable... particularly if an extra few hours won't impact the goods and it may be cheaper to land further away from the end user