There are many reasons that people will suggest not to use a framework.
- You will learn a lot by writing your own. I have been working on my own and I have learned a lot of different things about PHP that I did not know before. Overall it is a great learning experience that can be used in an interview or on your resume. It shows that you have a big interest in the language and most importantly the theory behind it rather than just the mindless implementation.
- There are a lot of things in frameworks that you do not need and by making your own you can get only whatever you want. The framework is tailored to your own needs specifically. I for one did not like how any of the frameworks handled templates which was the biggest trigger for me to make my own.
- Also, I am not positively sure about this one, but thinking of it logically...your own framework that is tailored to only your needs will be much faster than any of the other frameworks. Think about all of the settings that the other frameworks have to go through when loading and the database queries that involves. You save yourself all of that loading.
- If you are going to be making a small project that will not need to be expanded on, such as a simple portfolio website, then a framework would just be more work than necessary.
There is also a very good article here that goes into other details. The author of this article starts out by talking about how he always was such a big proponent of frameworks.
http://jpst.it/jiYX
I am always going to push towards making my own frameworks unless I start doing some freelance work. I am constantly updating my framework and learning more and more. You will never hear anybody say definitely use or definitely do not use a framework because it all depends on the use.
Edit: There is also a question over at the Programmers site on this: https://softwareengineering.stackexchange.com/questions/49488/when-not-to-use-a-framework
Edit #2: One last article about why frameworks are not necessary: http://www.amberweinberg.com/you-dont-need-a-framework-if-you-have-a-good-developer/
