Why don't videos sync to iPhone Photos?!

Hello.

I recently used to drag .mov, .mp4 and .m4v videos to my Photos app on my Yosemite iMac and those videos would, as expected, show in the iMac app and at the same time would sync to my iOS 8.3 iPhone 6 and iPhone 6 Plus Photos app. Now, when I do this procedure, the videos would show in the iMac Photos app all right, but without syncing to my iPhones.

What seems to be the problem? I'd appreciate good help from anyone!