Because either Unity 2018 or the oculus addons have seemed to be A RIDICULOUS MESS. Is carmack still at the company and does anybody at the company care that the tools don't function? (or did caring about the products leave with palmer? That would be mildly reasonable, but still...I have a Gear VR)
If there is ANY KNOWN AND VERIFIED method to ABSOLUTELY build and deploy a Gear VR/Go apk PROPERLY and WITHOUT ANY red console errors, post how here.
Our engineers have found that any Oculus packages within the Package Manager can cause a critical conflict within the editor. I've gone into more detail in the following post: https://forums.oculusvr.com/developer/discussion/72474/unity-alert-issues-with-2018-3-and-package-manager-01-03-19