It always felt like it wasn't the done thing to axe Cilla, so even when Surprise Surprise was axed as a regular series, they were really quick to point out that they'd still be doing specials, which they did for many years, and even though Moment of Truth was a pretty big flop, they kept on bringing it back in the hope it would come good, rather than having to axe Cilla. Even in The Fight For Saturday Night, Paul Jackson suggests they told Cilla's people it might be nicer for her to jump from Blind Date before she was pushed. She was so important to ITV at the time, they could never bring themselves to see "CILLA AXED" headlines.
She had a long term golden handcuffs deal with ITV (via LWT). That contract (either new or extension) are negotiated when times are happy, and the ratings are high. Future is looking good. You can ask for things to be inserted into the contract knowing that it'll never happen.
Wouldn't mind betting that there probably was a 'number of made and aired shows per year' clause put in it. With a hefty penalty payment from ITV if that wasn't met.
Cilla's two regular workhorses 'Surprise Surprise and Blind Date' slowly loose audience interest and show signs of grinding to a halt, LWT knowing the 'number of shows' contract, scrabble around looking for new formats, and reduce Surprise Surprise down to specials - just to keep its side of the bargain.
With the beancounters taking over the programmers offices in Kent House, they would look at the contract and get her to make any passing format, as it would be cheaper to make those with her fronting it, than to axe the existing programmes and have to cough up for failing to meet the clause in the contract.
Never did quite work out why we never had 'An Audience With Cilla' either. You'd have thought she'd have been a shoe-in for that programme.