It’s my responsibility into the later and me assuming their responsibility in the former.

Unexpectedly becoming the sole caregiver of an aging parent seems different to me. I can imagine some resentment, especially if it’s unexpected _and_ one is already the caregiver for their own spouse, children, etc. It changes your life plans, adds additional daily stress in your life, and may also add financial stress.

Another aspect possibly driving this: In USA a lot of people get divorced immediately after a cancer (or similar) diagnosis. That way only one of you goes bankrupt and you get to keep half your lifetime savings.