1. May 2014: OneWeb (formerly 'WorldVu') receives its initial $500 million in funding [1]
2. January 2015: SpaceX's satellite constellation is announced. [2]
3. December 2016: OneWeb receives an extra $1.2 billion from SoftBank and existing investors [3]
4. March 2017: Blue Origin signs OneWeb as a customer [4]
If SpaceX was a neutral transport provider, there's little reason that OneWeb would have chosen Blue Origin over SpaceX. Blue Origin is probably offering very low prices, but SpaceX arguably could match them.
[1] https://spacenews.com/40736google-backed-global-broadband-ve...
[2] http://old.seattletimes.com/html/businesstechnology/20254807...
[3] http://fortune.com/2016/12/19/softbank-oneweb/
[4] https://spacenews.com/blue-origin-gets-oneweb-as-second-new-...
As to why do it themselves as opposed to just be a provider to OneWeb, I think this is a sneaky way to do some price discrimination - SpaceX, like everyone else, may have some spare launch capacity, so having an internal (hopefully-profitable) project to soak up that demand rather than cratering launch prices may be worth it.
If Starlink, OneWeb, etc were cancelled tomorrow, it's likely GTO launch demand would pick back up significantly.
Starlink is both the cause of and solution to this problem.