My not so cynical view of the argument would lead me to suggest that "immigration" is an easy and short-term solution to the fertility problem. It's kinda hard to have politicians look at "generational" solutions to problems as the very nature of having politicians is that they "tweak and turn" random knobs to "fix" stuff that we ask them to. The rest is up to us as people and that is why cultural solutions mustn't be discounted entirely and political ones need to support that rather than being full-blown replacements.