It was the closest state in 2020 and had been associated with right-wing politics from Gingrich onward. Losing Georgia was a very bad omen.
Also associated with stealing power from black people since 1865
Probably because it was fully run by Republicans at the state level, and because of that, he thought he could get a sympathetic audience.
Why didn't those state Republicans oblige?
Georgia Republicans don't fear Trump. Their power comes from the Atlanta corporate culture (Coke/Delta/UPS/Home Depot). Not MAGA voters. Considering they won primaries in 2022 shows that.
Plus, Trump lost. Why should they fear him? In three months, he would be out of office. Even if they stole Georgia for him, Trump would need Arizona and Wisconsin just to force a house vote.
Finally, I like to think they wanted t be on the right(ish) side of history