When people talk about `cargo` being awesome, they're comparing it to the similar tools for, say C++ or C or other systems programming languages. No one is comparing `cargo` to `pip-tools`.
I haven't used pip-tools, but I have used pip, npm, bower, and other more modern dependency mangers that work for non-systems programming languages. Cargo has never given me any trouble. Pip has occasionally given me weird issues about things not being installed in the right places or on my path. NPM regularly required `rm -r node_modules` and starting from scratch. Bower has had the same trouble as npm. It's not that these tools don't work for me, I've always been able to google the error message and find someone with the same problem. It's that Cargo has never given me an error message that wasn't my fault like "This package doesn't exist" when it's a typo. It just works.