Mike Ryan's interview with Charlie is on Uproxx, and in it Charlie discusses why we haven't seen more films from him, and what happened to Frank or Francis.

Kaufman: [Frank or Francis] could still happen. It would have to be reinvented, though. We had a whole cast and we were headed into pre-production. So, I’d have to get people back and who knows if they would be interested anymore. But, at this point, we don’t have any money, so that’s a secondary concern.

[...]

So, if you had given your scripts to other directors, you could have gotten two or three movies made in that timespan?

Kaufman: Absolutely. Just because I had the most extraordinary cast for Frank or Francis. Extraordinary. I mean, it was like crazy. And the reason I kept hiring more and more crazy, well-known people was because it was the only way I was going to get any money. Even then I couldn’t get money.

I don’t understand how that happens.

Kaufman: Well, you know, 2008 was a disastrous year for the economy. Everything changed in the business after that. No, really. Sony Pictures made Adaptation. Not like Sony Classics, Sony Pictures made that movie. They would never make that movie now. It’s impossible for them. It’s a different business. And if Synecdoche made $100 million, it would be a different issue. But, it didn’t. (Source)