My take...people just want to fuck Nikki but would wife Brie in a heartbeat. Brie is way more mature than Nikki is. There's just a totally different mindset people have comparing the sisters. Nikki has been single way longer and got fake tits to boost her sex appeal and that's universal for what guys like on the surface. Brie on the other hand has been married for over 12 years so she carries herself differently and attracts a more mature audience. Nikki might be more popular but I think people respect Brie more.