"¿Vienes acá todos los días?"
Translation:Do you come here every day?
Basically, both acá and aqui refer to something close to the speaker. That much is clear. However, my sources appear to conflict a bit as to how they are used. Some say acá is used with motion verbs and aqui is used with non-motion verbs. Other sources say acá is used in a more general sense of here while aqui is specifically this spot. Not sure which is right or if this is a regional thing.
The adverbs for distance vary quite a bit throughout the Spanish-speaking world. Here is the link to the Butterfly episode on the topic:
If you Google it, you'll find a huge number of conflicting opinions, pertaining to usage and region. If you're looking to speak a specific version of Spanish, I'd try and learn the subtleties for that dialect and simply stick with them. Be wary of any "right answers" to this problem, as native speakers from different parts of the same country seem to have completely different opinions on the matter.
They effectively mean the same thing, but daily tends to be used to denote a scheduled occurrence (we have a daily meeting), whereas "every day" does not. Note, don't confuse this with "everyday" which means casual/basic/usual.
Also, your question. Should be "why can't I say..." or "why can I not say...". "Why cannot I say" is technically gramatical, but it's not a phrase anyone would use outside of poetry or other heavily stylized communication.