At a guess I expect its because the VC has vetted the business model and saves amazon from doing the same. e.g. if accel, a16z etc have stumped up seed money or an A-round it means the company would have a tested model, or at least one sufficient for them to throw serious amounts of money at. This saves amazon from having to do the same and allocate resources to vet the founders and startup themselves.
I honestly don't see the point of this (especially paid), when a browser based calendar with notifications enabled gets you all of this for free. I guess privacy is one consideration, but I already have a system there, I just use shortened words or prompts that only make sense to me.
I am not alone in doing [2], in fact I found out its a national tradition in Bhutan: https://medium.com/the-ascent/in-bhutan-people-think-about-d... - it sounds strange and I am not I recommending it to everyone, but it's totally changed my mindset on life and dissolved my depression and anxiety. I find when I focus my thoughts on the fact that I will die, and I have no idea when that will be, I feel a profound deep feeling of gratitude. The small trivial things don't matter anymore.
Two the biggest dysfunctions we have in western society are worship of youth and an irrational fear of death, to the point we don't feel comfortable to speak about it. We would rather pretend it does not exist and happens to other people.