The reality is that companies these days will take the employees if they need them under TUPE and if there is no need they will all try their utmost not to because of the cost & issues involved.
As we all know if people are doing the same job and some are getting better terms & conditions after being TUPE'd across that this will create issues.
I heard that in the past that some companies who lost a contract increased terms & conditions just before the TUPE'ing across happens, which if true might be another reason why the other company is reluctant to take employees across.