The same reason why you can't give them cash or gifts; it's considered bribing.
Again....you either think people are too dumb to bring a bottle of water, or they have get it 25 feet away from the line..., or.....
poll officers are allowed to make available "self-service water from an unattended receptacle to an elector waiting in line to vote
And it's perhaps worth noting that there is not a prohibition on voters in line buying food and drink for themselves
the provision is about other people providing "money or gifts" including food and drink
Again, read, comprehend, learn.
https://www.wrcbtv.com/story/43587651/fact-check-what-the-new-georgia-elections-law-actually-does
“The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is.”