You might need a time machine to give a better experience to someone long dead, but not to give them more of what they wanted. For example, if they wanted to be remembered and revered, we can do that for them today. But we don't do much of that, for them. So we don't need time machines to see we don't care that much about our ancestors. We do in fact have conflicts across time, where we each time would prefer allocate resources differently. That is why we should try to arrange deals across time, where for example, we agree to invest for the future, and they agree to remember and revere us.