Two problems FLB. Firstly the money - I'm sure he would have gone, or will go, given an offer around the £5/6m mark. Apparently Rangers haven't been near.
Secondly, the timing. We're in real danger of relegation and to lose him without a replacement would be suicidal IMO.
As for him not putting the effort in if has to stay - no-one knows that, do they? The people best to judge that are Hughes and JW.