Neither Air China nor Korean gave their Lgw service much of a chance so I am not sure how they could decide so quickly.
They have the commercial data which compares their LHR vs LGW operations. The LGW services seemed to attract the lower yielding tourist trade with the front end prefering LHR. Remember that the US airlines who moved to LHR in 2008 said they would operate dual LHR/LGW but both US and CO dropped LGW soon after and DL did in the end as well.