No casting button in apps that should have Chromecast support?

[MRW1215]

I'm noticing that apps that should have the casting feature don't have a casting button anywhere that I can see. The only apps I use that I have a casting button are Netflix and YouTube. Doesn't Google Play Movies have casting support? Doesn't Hulu have casting support? And supposedly, HBO Now has updated with casting support. But none of these have a cast button for me. Is there a reason/ fix for this?

I'm on both a Nexus 6 and 7, both rooted and running custom ROMs, if that matters.