Because this has been a topic of conversation on these post: Blaming of Verizon or Microsoft concerning the reasons for disabling the CDMA bands on the Lumia 950(XL). The comments after the articles are also interesting.

Surur of WMpoweruser puts it Microsoft. The commenters disagree: http://wmpoweruser.com/microsoft-shares-blame-for-the-lumia-950-verizon-issue/?utm_source=feedburner...

Winbeta puts it back on Verizon:http://www.winbeta.org/news/verizon-reported-blocking-network-access-lumia-950-950xl

You all can form your own opinions. It is clear to me, and the majority agrees, Microsoft disabled it because of how VZW treats Windows Phone.