It costs money for an empty positioned so say it went to MAN but the aircraft is then needed in LGW then it would cost them double than when it positions out as required as a backup.
Stand 10 can also accommodate a B767 and B757 if required. Also be better not to block up the only proper remote stand 6 as it is required for widebodied diversions such as B777 or B747 if required.
I know Echo can be used however once again it can be used for large diversions. Also don't forget when the aircraft parked up it was probably thought it would have been gone within 24 hours as usually is the case.