Likewise similar to your DM and DF, our neighbours, who already had two decent cars, took a new motability "fun car" when one of them became disabled - no special adaptations, she still used her original car perfectly fine, but took advantage of motability to use her DLA/PIP (or whatever) to have a little "fun" car. It's that kind of thing that's draining the money. People claiming things they don't actually need, just because they can, and no doubt, being "pushed" into it by healthcare/social care workers.
When my OH was first diagnosed with cancer and was put on the track for a stem cell transplant, he had a couple of "consultations" with support workers from the ocology department advising him on what benefits he could claim, (DLA or PIP) including a free hospital car parking permit, blue badge, etc. The thing was, he was, and remained, perfectly capable of working, walking, paying for car parks, etc., so he declined it all as he didn't need any of it and couldn't be arsed with the paperwork, getting doctors to sign off forms, etc - he had enough trouble getting the doctors to actually arrange tests/treatments etc and really didn't want extra stress just for extra money that he didn't need. He said at the time, he'd defer claiming until such time that he had to stop working, and 7 years later, still on monthly chemotherapy, he is still working, so still doesn't claim anything.