why does my phone get slower

[afail]

Ok I know this may seem like a dumb question, but here me out

Regardless of how many times I soft boot my device, this phone just degrades itself after a hard reset.

I don't really have a lot of installed or running programs (in fact I actually have 15MB of free ram at all times) but just things like text messaging get really slow and eventually i am typing faster than it can keep up with

Does the phone fragment like a hard drive? other than e-mail and texts and the occsional opera mini use, i don't use the phone for anything else. Soft resetting doesn't seem to fix it.

So again this may seem like a dumb question, but why is my phone eating itself?