No-one is suggesting that ALL should go down to Goodison at all. Just some who live on, or usually use that East Lancs/Walton Lane corridor, as their public tranport journey doesn't give direct access to the BMD site (nor the Scotland Rd drop-off of most North-end bus routes, as it turns up Robson St off Walton Lane), and access via city centre shuttles would be convoluted and feel like going-back on themselves. The area around Goodison could also provide a familiar park and ride option for some out of towners, most importantly keeping more cars away from the immediate vicinity.
I agree about the "speedwalking" assessment of the walk to/from Lime Street by Mr Drone, he was almost jogging at some points. Plus of course it could take a further 5-10 mins or more just to get out of the Everton plaza post match. Lime St is literally only a few hundred metres closer to BMD than it is to Goodison. It is of course a very doable walk for the able-bodied and can be broken-up by using various bars and other amenities, but hardly convenient or great in accessibility terms, and less than conducive for the required modal-shift to public transport for those who simply want to go the match, then get home asap.