The Magicians is a SyFy original series based on a fantasy book of the same name. It's essentially a deconstruction of the young-adult fantasy genre, aimed squarely at grown ups (it includes obvious send-ups of Narnia and Hogwarts).
The show has some pretty adult themes: there's an absurd amount of sex between all variety of participants, lots of death, depression, addiction, etc. Plus, there's a lot of swearing. Every episode contains multiple lines of dialogue where characters use obscene language, and the worst of it (primarily the "f-word") gets censored out.
It's that last part that confuses me. As far as I can tell, the show was written and produced specifically for the SyFy channel. Unlike many of SyFy's shows, it's not an Australian or Canadian import. It was produced by a US company, by people who have extensive experience with American network TV (one of the EPs worked on Supernatural for 6 years).
Why would they write and film dialogue that they knew would never be allowed to air on the network they sold the show to?