Why are many theists so ungrateful for the one life they have?

You have only one life. Its short, finite, and relatively insignificant in the grand scheme of things, but its the only one you've got and because of that it is precious and irreplaceable. Who are you to demand a unlimited second one? That's got to be the most selfish thing anyone could demand. What makes you feel so special, that you should feel ENTITLED to a second, unlimited life? That you should waste the one life you have on nothing but preparing to get another one?