This is because it keeps leaping to new and richer axes.
Eternal life means having time to read forever (as new books are forever being written)—but no one in heaven actually does this, or not JUST this, because books are not meant to just be read, but to complement an actual life.
Eternal life means having time to explore (and renovate!) the universe forever—but no one actually does this, or not JUST this, because it is soon found that exploring and renovating are components of the good life, rather than comprising it.
Eternal life means having infinite progeny, worlds without end—but no one actually does this, or not JUST this, because joy requires much more than numbers.
And lest you imagine that it’s just an ever-accelerating parade of Kuhnsian paradigm shifts, leading to future shock—all of this is measured and evaluated in terms of relationships.
There are many different infinities, indeed an infinity of infinities—the natural numbers, all the real numbers between 0 and 1, the set of all possible books, the space of the universe, all possible paintings—but some of them are better and richer than others. It would be a poor life indeed (though infinite!) that consisted of counting the natural numbers.
Heaven is to our conception of it, as the set of all books is to the set of natural numbers. But more so. And the gap is ever widening.