IMHO Everyone should write at least one framework of some kind. Bonus if it's open source.
It's a huge learning experience. Gives you a deeper understanding of how other other frameworks work. Helps you understand user and customer support. How to write documentation. Great for your resume. Etc.
In other words, if you only ever consume frameworks it makes it difficult to know what to do or how to approach solving some of the lower level issues a framework may present.
Do you have any personal experience in doing so? They seem like tempting projects from the outset, but getting started with some clear goals in mind, alongside philosophical/idealistic differences from what's already out there so you're not simply rewriting something for the sake of it has prevented me from getting too far down a particular rabbit-hole.
My first php framework was something called php4gl back before ruby on rails was created. It used the command line to bake controllers and such. Just a private project never released. Lost the code now!
I also wrote another couple more php frameworks. I used one for all my personal side projects. And I wrote a couple for day jobs website over the years.
Actually it wasn't until Laravel came out that I was convinced NOT to write or use my own php framework ;)
So, now I've stopped writing php frameworks. But, I still write a CSS component framework from scratch for every project.
I wrote a really quirky javascript framework called Double Dollar that worked using a kernel pattern. Anyone I showed it to thought it was nuts. I abandoned it and now just use jquery for projects I work on like https://nugget.one
Probably the most sucessfull open source project I created was ezSQL. Wordpress ended up using it as their original database class and then as the API interface for their current wpdb database class. I think a lot of people probably curse me for that ;)
It's a huge learning experience. Gives you a deeper understanding of how other other frameworks work. Helps you understand user and customer support. How to write documentation. Great for your resume. Etc.
In other words, if you only ever consume frameworks it makes it difficult to know what to do or how to approach solving some of the lower level issues a framework may present.