I think she's probably just running out of new ways to photograph or make videos of her long hair. She's got a ton of material as it is, and even among her current stuff, there's a ton of Part 2s of earlier works.

Since her hair doesn't seem to be getting longer, new videos can feel repetitive. She's also a professional with an active life, and as one gets older it gets harder to devote extended periods of time to hobbies. I wouldn't worry though. I'm sure her hair is still very long and lovely.