The Pacers were simple, generally reliable, and cheap both to lease and operate - and, shock horror, actually perfectly adequate for plenty of routes.
Travelling on a Pacer was no worse than travelling on a Class 150 still is today, and will continue to be for some years to come. Their withdrawal was primarily a political move, driven by a vocal few with certain agendas. I very much doubt that the passengers of Northern or TfW, who were crammed into short formed services in the middle of a pandemic, thought that their withdrawal was so vital that it was sensible to push it through despite there being no replacement ready. Given the multitude of hurdles that have beset numerous fleets of eye-wateringly expensive new trains, there is a lot to be said for the simple, fit-for-purpose approach of a train like the Pacer.
End of rant!