There's no sprinting for balancing reasons; it's very easy to rush already as Pointman, and adding sprinting would exacerbate that issue even more. Think of it as you're always sprinting, and when you hold shift, you're walking instead.

In regards to putting a sentry down again, what do you mean? You can relocate a sentry as much as you want, you only lose it if you allow it to get destroyed, and if there was a way to easily get your turret back, that would defeat the purpose of them being destroyable.

not every game needs a sprint, did you suggest this for L4D too?