After years of trying to get my parents to use Skype, they have willingly adopted Duo. I'm not sure if it's ease of use, or reliability, or one being associate

After years of trying to get my parents to use Skype, they have willingly adopted Duo. I'm not sure if it's ease of use, or reliability, or one being associated with desktop and the other with mobile, but they call on Duo even if I say "Skype".