Yes, there are reasons for reduced frequency (largely to do with me frankly) but Popup Chinese is not going anywhere. We've never been able to produce enough to avoid some complaints, but have more and better materials now than ever, so we ultimately are what we are.
We have another dialogue recording session this weekend, so things are ongoing and if there is anything you'd like covered that we've missed please do email with suggestions. Realistically, we are at a point where we have covered so much it is challenging sometimes to find new things to teach. And it can be difficult getting good dialogues as well.
In the meantime, If people want to help the obvious ways are linking to us or contributing with word or mouth. Popup Chinese is very much a labour of love, but more resources do translate into being able to hire and produce more. That said we are not really the most commercial organization and consciously avoid trying to maximize revenue (with email spamming, recurring billing, limited free stuff, etc) when it comes at the expense of the sort of place we want to be. The same goes for producing content we're not happy with, just for the sake of volume.
That said, I don't think you need to feel guilty or worried.