I work with an enterprisey on-prem product, which we of-course tried to replace with a cloud offer. And in all fairness, it's generally gone well - but because we manage the platform, it sits in the cloud we chose. And that's never going to be the right choice for everyone.
So we have some customers who are concerned about national boundaries. We have some customers who offer their own clouds, and aren't hugely enthusiastic about using the competition's. And then the whole mess with the govt having isolated regions within otherwise-public cloud offers.
Between these, it quickly became apparent that replacing our traditional offer with *aaS would leave a lot of money on the table. It's a minority of customers, but it turns out to be a very valuable minority.
Within that context at least, "private clouds" start to feel like they have legs - bringing most of the benefits of the cloud, to places that 'public' can't reach.