> I am honestly surprised they keep pushing this
I'm not surprised. One of the big problems that faces Netflix is market saturation. Lots of companies like Google or Facebook can grow profits by getting you to use their service more. The more you use, the more they earn. Netflix can only get more revenue by getting more paying users or raising prices on existing users.
In the United States and Canada, Netflix has 74.4M subscribers. The US has 124M households and Canada has 15M (139M total). 54% of US/Canadian households already subscribe to Netflix. If each of those paying subscriptions is also being used by a second non-paying household, that means that 100% of US/Canada has Netflix. If that's true, the only way for Netflix to gain revenue would be by raising prices or eliminating the account-sharing and hoping that more people will be paying customers.
I'm sure Netflix has run the numbers based on their internal data. They already know who is sharing accounts. If 50% of accounts are sharing, that means that the 74.4M subscribers becomes 111.8M households and 80% of US/Canada. Basically, Netflix should know how close to the total number of households already use Netflix (even if they aren't paying for it).
If 80% of households already have access, you've basically hit your growth limit. You can't expect 100% - only 87% of households have broadband internet in the US and some people just won't be interested. It seems reasonably likely that Netflix is pretty close to their growth limit in the US/Canada without going after account sharing. If 50% of accounts are sharing, they've probably hit 90-95% penetration in the US/Canada given that 13% of households don't have the internet required for Netflix.
I'm not surprised simply because it seems like the only avenue of growth for Netflix in many markets. Netflix doesn't charge you per show. They don't have add-on packages for sports or whatever. If you love your local take-out place, you might order from there more. If you love Facebook, you watch more of their ads. If you love Netflix, you don't buy a new account each day. To keep growing in many areas, Netflix needs to break up account sharing.