FGW▸ took the decision to terminate this train at Oxford and as there is no way of getting the stock to Malvern (and no spare stock anywhere near Worcester) to start the working that stops at Worcester at 0852, the train did not run.
It doesn't even have to hitch a lift as Will has just suggested, though that's a nice neat solution now that the 08:52 ex Malvern is a Turbo, and would mean that Evesham and Honeybourne would also get their train as advertised.
What has happened in the past is that the Turbo runs empty from Oxford to Moreton after the 06:43 Hereford to Paddington clears Wolvercote (approx. 08:45) and before the next down working at 09:21 from Oxford. There's a surprising 40 minute gap in occupation of the single line from Wolvercote to Ascott at this time of the morning which gives ample time to let this Turbo run through in time to return from Moreton on time at 09:50 - at least the punters from Moreton, Kingham, Charlbury and Hanborough then have a service as advertised.
It obviously might not make sense if there is disruption to the Up trains, but if everything is reasonably normal then I see no reason why every effort should not be made to do either of the solutions above - however, it seems very hit and miss and might just depend on who's on shift making the decisions at Swindon.