The US has no national security threats in its region. Conscription would only be about fighting a war with China, which would be a war of choice (like all US wars).
You can relatively easily conceive of scenarios where the US either needs to directly confront China, or lose its geo-strategic preeminence, but it much much harder to conceive of scenarios over the next 50 years in which direct confrontation with China is 'actually existential' (in the sense that if the US loss or did not partake in the confrontation, that the US would domestically cease to exist in a recognizable form).
Effectively, the US' challenge for recruitment (and honestly a lot of things) is to convince enough of its population that US hegemony/preeminence is "a good thing" and worth fighting and dying for.
Too bad the US pissed away a good chunk of that capital with GWOT.