Once TfW have accepted each 769 into service, they've been paying leasing charges on them. I think TfW might have even had to start paying leasing charges once they accepted the 769s to have them out for crew training.
If we lived in a BR-era simply structured railway, where DMUs could be moved around freely, there's no doubt the 769s would've been gone by now, with something else brought in instead, like some more 153s from the glut that are being retired at the moment. But we don't. And the 153s being retired by TOCs in England are not PRM compliant. So the 769s will have to limp on until the Stadler Flirts start to arrive.