A couple of years before he died, he suddenly married. The woman was a young refugee who also had a family in another country. His death was sudden and unexpected, although his health wasn’t great (in his seventies, so he wasn’t particularly young).
It turned out her DDad had made a new will, leaving everything to the new wife. The woman wouldn’t even give SIL any mementoes from among his stuff - she sold the lot. All SIL was able to do was go and rescue her DDad’s beloved, aging cat, which new wife had turfed out of the house and hadn’t even fed. As soon as the house was sold, new wife disappeared.
SIL found the whole thing utterly distressing. The sudden marriage and will change were so out of character for her Dad, who had always doted on her and had never taken any of his romantic relationships seriously. She was left wondering if he’d been coerced, or had genuinely just had his head turned by this young woman forty odd years his junior.
Call me a cynic - and I'm not saying that massive age-gap relationships are never, ever genuine - but I think that, in such a scenario, the intentions of the younger spouse are extremely clear to understand; when we're talking a gap of two generations. Obviously, you'd have no desire to marry your own actual grandparents - but would you ever see your grandparents' friends as attractive romantic partners? Really?
Without wanting to sound crass, I think they see it as an investment - maybe even just as a job, essentially - whereby they provide romantic/sexual and whatever other services for a person old enough to be their grandparent, who has significant assets; also putting on hold their opportunities for happiness with a partner their own age during that time - in exchange for a hefty payout after likely not too many years.
It would be amazing if they didn't expect to take the maximum return on their 'investment' when the time came. And surely the much, much older spouse must also fully understand what the deal is, and how it will play out after their death.
That said, it's extremely callous beyond words - in this and other scenarios - when somebody's greed extends far beyond the property/money/valuable assets, and they also deny the deceased person's family the old photos, mementoes, personal trinkets and sentimental items that mean the absolute world to them, but are worth nothing more than a couple of quid at most to them or to anybody else.