I would think most of us have stuff on our devices we wouldn't want others to ever be privy to, and if not for our own privacy, then for that of anyone who had contacted us or exchanged information.
I don't think it's a matter of something that shouldn't be on there in the first place, for instance, I don't have anything illegal in my possession, but just embarrassing and humiliating and senseless to anyone who isn't me.
I just don't feel like being misinterpreted by my own words or images or having people use anything to do with me, to their sick benefit once I'm dead.
My data would be safer in the hands of a stranger (who would likely have no use or interest in it) than my own nosey, self-important relatives.
Conversely, if any of my family members suddenly died, and I had access to their devices, I would smash them before anyone else got the chance to pry, no matter how badly I might want to look myself (save, for maybe, my mother..but I still wouldn't let anyone else snoop unless they wanted their texts/pics deleted from her phone, in which case I would oblige).
Unfortunately I care a great deal and I'm already trying to strip physical items and pictures of myself from my family's hands while I'm still alive, I don't want them having a free-for-all with anything I may accidentally leave behind. I want to erase myself as much as humanly possible, because I don't trust a single one of them to respect my wishes.
Once I'm gone, it will be all about them, not that that's any different from now, I just won't be there to protest or assert my rights.