BA had a debacle at LGW and have had to effectively bring their handling in-house due to the collapse of their handling agent
They got their own formerly loyal staff back at much cheaper rates, on a monopoly contract and off the mainline books! Not intentional obviously, just a happy accident.....
Jet2 self handle their own operation to make sure they can have the right degree of control, as soon as they start to handle another carrier, those reigns loosen and the focus on Jet2 ops slips. Depends if they see it as a a
cost centre (which it really is) or a
profit centre (which it's not). The only killing made in ground handling is to terms and conditions.
As for Ryanair, the most cost conscious of them all self handle at Dublin and have done for years. Do they self-handle (ooer missus!!!) anywhere else on the network?