Do you have any credits with Archion to check whether the marriage was duplicated in the Burgstall register? You would need to look in the Mischbuch 1599 - 1738.
We can only ever speculate about why our ancestors chose to marry in a certain location; that applies in any country and in any period. In this case, I am certain that the fact that the bride's father was the mayor of Burgstall, a respected pillar of the community, must have played a role. One can imagine that he arranged quite a sumptuous wedding. Furthermore, it's reasonable to assume that Anna Maria was living with her father in Burgstall at the time. What makes you think that she was somewhere else?
Did the happy couple have any children? If so, where were they baptised?
Archion has standardised the descriptions of the registers. You would need to look at the original records to see the title used by the vicar who maintained the register. Eheregister, Heiratsregister and Trauungsregister are all the same thing. In early registers, you will generally see the term Copulation, and the couple copulirt.
