Cardiac glycosides are deadly toxins.
U.S. citizens who make regular use of cosmetics containing cardiac glycosides are probably unaware that the product desperately wants to kill them. It seems unlikely that rational persons would slather themselves with cosmetics labeled as "rat poison", yet every day they slather themselves with rat poison labeled as "cosmetics".
Notably, the European Union has banned over 1000 substances from cosmetics, cardiac glycosides among them (EC no 1223/2009).
There is no compelling reason for cosmetics to contain chemicals that affect cardiac function. However, there is a compelling government interest - product safety - for outlawing them.