Maybe his legal team believed that he would almost certainly be found guilty anyway because the weight of evidence against was such that there was very little chance of acquittal, and that an early guilty plea would reduce his sentence.
None of these cases are the same. Just bcause DLT has been found not guilty does not mean Freddie Starr will get the same verdict. OK, we have had two or three acqittals, that is not necessarily the pattern. The next 3 that are heard might be guilty verdicts.
Historical cases are very difficult to prove and to gather evidence for.
It didn't help Gary Glitter or Jonathan King. Perhaps they were has-beens and had slipped off the z-list. I suspect that Stuart Hall comes into the same category.