Why doesn't Marketo show my webinar attendance?

We've had that issue too with WebEx and it sometimes takes 1-2 days for the attendance data to sync over from WebEx over to Marketo.

You can try refreshing from your webinar program in Marketo although that never seems to work for me...just have to wait it out.

I was going to say the same thing as @Nina Valtcheva​ - We use On24 and I have to refresh from webinar provider about three hours after my live webinar. Also, many times it doesn't take the attendance record in account until you schedule or trigger to run your post-webinar programs/campaigns if you do so. For example, my attendance record doesn't always sync until I schedule my batch campaign to send out follow-up emails and I can see it in the "schedule" tab for how many people attended the webinar and will receive the email.

But, when in doubt, refresh from webinar provider should work.