I think both PHP and Ruby still have and will keep their niches, but in my opinion they don't provide the building blocks to expand outside of their niche and grow much at this point. If you contrast that with let's say Rust, which at least has the potential to become successful across a wide field of applications.

The problem that I can see with Ruby in particular is that its niche is getting smaller and smaller as the world evolves around it. Interactions with external services that are on the critical path to serving requests are becoming more common. Interactions with actual contents of pictures and documents are becoming more common. Concurrency is a major missing building block to build modern apps compared to 10 years ago, and the answer of the Rails community has mainly been YAGNI (although there are efforts to incrementally improve things, but no fundamental shift in language or runtime design).