I assume out of town shopping was/is a strategic decision by the council, who therefore have to shoulder the blame for the state of the town centre. Same shitty administration getting in despite managing an impressive levelling down agenda.
Not sure whether it was any sort of strategic decision, just a muddle that planning (which failed to consider the long term) got into in the late 70's and 80's with Swindon being one of the first places to really embrace it, I suspect as much as anything as it coincided with the town growing at a frantic rate, possibly without the benefit of a strategic master plan.
As for shouldering the blame, it can't all be laid at the door of the Council, they might have allowed out of town shopping, but its not compulsory for people to actually use it at the obvious detriment to the town centre. See also, and I'll say it again, pubs and rural post offices.
Still ongoing in some places too - google "15 minute city" (Oxford, Bristol, Canterbury and Sheffield are trying to head that way)
They really aren't what their detractors are desperately trying to portray them to be, they have just been grasped as another battle front on the incessant and tedious culture war that some politicians and commentators are peculiarly so keen to perpetuate.
https://www.newstatesman.com/quickfire/2023/02/fifteen-minute-cities-will-be-back-conspiracy-theories-house-commons