I think many if not the majority of Americans would care about this if they were aware of Obama’s inclination's. As to being “too long ago, “ given Obama’s age, how long ago could it have been? As to Communism not being a “threatening” ideology, the deaths and enslavement of millions by Communist regime's testify to it's threat to life and liberty.
People will not perceive Communism as a real threat unless it has some chance of taking over. Which at present it does not. So they don’t see it as a threat, but rather as one of dozens of competing wingnut ideologies espoused by losers.
Examples: American Nazi Party, Scientology, Black Liberation Theology, the New Black Panthers, the KKK, Aryan Nations, CPUSA, Christian Identity, La Raza, Al-Fuqra. Etc., etc.
Any of these groups would bring death and destruction in their wake if they ever became strong enough to take over or even to contend for power. Since none are at present in such a position, most Americans just don’t view them as a threat.
Possibly this is short-sighted, but America has a 200+ year history of being short-sighted to long-term threats. So far it’s worked out reasonably well for us.