Can't Build A Bundle

@suzieeful  Which game and stuff packs have you not yet bought?  The Werewolves pack is new enough that it may not be available for bundling either, so you may need to use a different game pack instead.

If this isn't the issue, please let me know whether you're using the Origin website or the app to try to bundle, and whether the other one works.  Please also list the packs you don't own, other than kits, which can't be bundled.

I'm getting the same thing. I still have Get Famous, High School Years, My Wedding Stories, Bowling Stuff, Kids Room Stuff, My First Pet Stuff, and Nifty Knitting Stuff, to get. I've been trying to bundle Get Famous, can't bundle, I get the "You're quite the collector! Because you own so much content for The Sims 4 already, we can't create a totally new bundle for you at this time. Please check out our individual packs to grab something new." message. I have one of each pack available to get. 
I've tried Origin App, Origin website, and EA App

@Aussie-Blue-Fox  My Wedding Stories isn't yet available to bundle.  That's a bit surprising to me, since it's been out for a few months now, and I'll ask around if this is by design.  But for now, that explains your issue.