The 700s on the Sevenoaks/WGC service aren't rotated that much, so that might explain how bad things are in terms of how badly they're hit. The toilets have been repainted and within a week, they're covered again. You'll quite likely see that they now cover the ceiling in the toilet and have taken to using white paint to cover the floor also. It's absolutely insane how bad these trains are being hit, and if repainting isn't stopping them then I wonder what will? Vinyls might work to a degree, but you'd need suitable designs/patterns to stop people just covering them and forcing new vinyls almost daily.
You'll probably also see that the 700s on some routes are now almost exclusively without the glass on the egress panels. On some trains, you can see the floor covered - and it can't be cost effective to replace them. Perhaps they will get the 717 style panels in the next refurb?
At the end of the day, they look terrible. People want them kept clean, but that comes at a huge cost. The cost isn't new paint, chemicals to clean paint, or vinyls, it's better policing of the railway - especially the Southeastern stations that appear totally lawless. There's no way you could fix this with penalty fares for anti-social behaviour if such behaviour is so far gone that staff would be in extreme danger. It would take strong police action, and months or years to alter behaviour to a level where you could patrol trains safely.