They were broadcast on different networks. Magnum PI was on CBS and the A-Team was broadcast on NBC. It would be more difficult than getting B.A Baracus on a plane to Hawaii!
I agree that would be an interesting idea for a Crossover but...
This is not the right place for this discussion because there is already a thread created to suggest and discuss possible Crossovers that we would like ,which may be written to read them: https://www.alternatehistory.com/discussion/showthread.php?t=338142