Streaming doesn't count for Billboard 200 and well Shake It Off which is a current single actually IS on Spotify.
Also, album and single sales (both of which Taylor isn't lacking) turn more of a profit than individual streams which are marginally very small.
Streaming would give people an option to listen to the album without buying it. Thus less money, and thus it will take more time to recoup their financial investment into the album.
If people don't want to buy it, they won't. It's better to have them stream from Spotify than to illegally download. All this does is annoy potential customers.