It’s good to point this out.
Though I do think Bluewater is an anomaly. I am surprised they are not curtailed at Dartford, instead all three TfL routes continue to Bluewater, with no contribution from Kent County Council I believe. It’s great they they do this (as well as linking areas of SE London to the Darent Valley Hospital), but I doubt this would be introduced if Bluewater was built in more recent times.
Three TfL buses run to Bluewater: the 96 and 428 run fast from Dartford town centre, stopping at Darent Valley Hospital only; the 492 is all-stops through Stone and Horns Cross. The hospital serves as an A&E for much of Bexley as well as Dartford/Gravesend, indeed the 96 running via DVH only came about eight years ago as part of a TfL plan to improve access to hospitals.
I had to use the Kent bits of the 96 and 428 daily for a couple of months last year: one thing that struck me was the number of people using the 96 to Bluewater and then taking the Arriva 700 towards the Medway Towns.
Bluewater's opening in 1999 pre-dated TfL by a year or so; the 96 was extended by Stagecoach as a commercial shopping-hours venture at first. It clearly worked as the entire service soon ran there, and TfL even extended the operating hours on Sunday mornings last month (the first bus leaves Bluewater at 0415 Mon-Sat and 0430 on Suns).
It's an incredibly important and very well-used link serving a unique combination of a a massive regional shopping centre and an important hospital. Dartford Station, Bluewater and Darent Valley are the first, second and fifth busiest stops on Woolwich-bound journeys: https://edjefferson.com/busiestbusstops/?route=96&out_in=outbound