Preach it!
The foundational languages of the web: HTML, CSS, and JavaScript are so flexible and powerful that most of these frameworks 'help' by limiting freedom of expression as much as they do promoting a standardized method for solving problems.
In reality, most of the problems frameworks claim to solve can be worked around by simply digging a little deeper into the language you're working with and making use of that extra expression you're giving up when you use a framework. I see it all the time with CSS, and so I can only imagine how much worse the problem must be for JavaScript (which is many times more expressive than CSS).
Every time you use a framework or a tool you're using an imperfect abstraction of the language it works with, so if you find yourself using two, three, …or ten tools to write code in one language it's probably not making it easier, it's likely limiting the scope of what you are free to express normally that would solve your problem, and instead you're left with only the overlapping parts of the language that all tools share in common.
It's really no wonder people get stuck so much the more tools they add to their stack!
Frameworks are excellent libraries of ideas, and sometimes even best practices, and also act as time capsules allowing developers to reference ways things were done at a certain point in time, or when needing to support certain browsers. New developers today may not be able to find information about how to support IE8 for example, but by reading through the source code of frameworks that support IE8 the techniques that they need will be demonstrated. The don't need to use the framework to learn from it.
When you are producing frameworks or themes based on a framework, which other developers will be further modifying directly.
If you have a team of developers with varying skill levels it can be more comfortable for junior devs to adhere to a strict ready-made system prepared by more senior devs instead of trying to make their own. Eventually the goal is that any professional developer working with a language would eventually be that senior dev who is able to create precisely the framework that is required for a project.
There may be other uses, but I think the way most frameworks are used as base building blocks for everything is turning software developers into 'quiltmakers' instead of 'weavers'. If the web was like a piece of clothing, some people are busy making fabric pieces and other people are busy stitching pre-made sections of fabric together. Maybe it's a time or energy savings to make a quiltwork out of ready-made parts, but you're going to have a hard time creating clothes that look unique and fit well when you're assembling the garment from the same patterns every else grabs instead of making your own patterns, or even cutting your own fabric based on those patterns without using them directly.