Okay, so elves aren't interested in sex or otherwise capable of producing children as quickly as others, which implies (along with other factors, such as the immortality itself) that they're not geared towards being a successful species.
Maybe, maybe not. If we look at the real world, it's the wealthier and more industrialized - which we often equate to "successful and advanced" - countries that have the slower population growth rates, while some of the more impoverished ones have the highest growth rates. Partly this is because in poor and/or rural areas children are economic assets that provide labor and income, while in wealthy and/or urban areas they represent a drain on money and resources instead. So, a look at population growth alone would lead one to conclude that Africa is more successful than Japan. If we were to judge by our own standards of success, the conclusion might be that the more successful a society, the less desirable children become. In other words, elves could be so content and involved in their own affairs that the investment required in raising a child becomes less desirable than the ability to tend their gardens or write poetry, or whatever it is Tolkien-esque elves do.
It's not a perfect comparison, what with patriarchy and capitalism and other sociological factors to consider, but it's evidence that success may be more complicated than the ability to out reproduce others. (It's also perfectly valid to argue that both Tolkien elves and countries like Japan are, in a biological perspective, stagnant and failing.)