Why did LEGO stop selling sets for <1.5 year old (Primo etc)?
I can't comment on why Lego stopped selling Primo. But I can assure you that Duplo is fine for children. The smallest pieces are way too large to choke on, as far as I can tell. Small babies probably don't know how to put the pieces together very well, but that doesn't stop you from building a little house or car or something and letting them play with it.