Actually, 2nd Fleet doesn't exist anymore either.
3rd Fleet - Eastern Pacific
4th Fleet - Central & South America
5th Fleet - Middle East
6th Fleet - Europe
7th Fleet - Western Pacific
10th Fleet - Cyber
and Fleet Forces Command, which isn't a numbered fleet (replaced 2nd Fleet), but still maintains operational authority over the Atlantic.
Following WWII, US had:
1st Fleet - Pacific
2nd Fleet - Atlantic
6th Fleet - Europe
7th Fleet - Pacific
All as active combat fleets.
As time went on however, that began to change.
Following the US' end in the Vietnam War, Pacific Fleet decided it was time to restructure itself, as it had both 1st and 7th fleets organized as wartime fleets. They decided to deactivate 1st Fleet, and restore 3rd Fleet (at the time a reserve fleet) to an active fleet for training forces for deployments.
As time went on, 7th Fleet began getting tasked with missions outside of the Pacific, notably with the Indo-Pakistani War of 1971 and Desert Storm. As a result, 3rd Fleet still maintained its place as largely a training fleet, but also maintains operational control over the eastern Pacific (international date line to the US coastline).
Continuing that trend, 4th & 5th Fleets joined, in order to reduce the amount 7th and 2nd Fleets had on their respective tables, leading to
2nd Fleet - Atlantic
3rd Fleet - Eastern Pacific
4th Fleet - Central & South America
5th Fleet - Middle East
6th Fleet - Europe
7th Fleet - Western Pacific
As information and cyber warfare became a new front, the Navy decided to create a wartime fleet dedicated to it, and enters 10th Fleet.
Continuing further, it became obvious 2nd Fleet was almost exclusively used for training forces for deployments to 4th, 5th, and 6th Fleets AOR (Area of Operations), and it decommissioned, becoming Fleet Forces Command, which was founded to be dedicated to training forces.
Honestly, I would suspect that within the next 10-15 years, 3rd Fleet is decomissioned, Fleet Forces Command is changed to "Atlantic Fleet Forces Command", and what was 3rd Fleet becomes "Pacific Fleet Forces Command", with both Fleet Forces Commands being dedicated to training forces for deployments to 4th, 5th, 6th, and 7th Fleet AORs. Basically giving you a:
4th Fleet - Central & South America
5th Fleet - Middle East
6th Fleet - Europe
7th Fleet - Pacific
10th Fleet - Cyber
Atlantic Fleet Forces Command - training for deployments to 4th, 5th, 6th Fleet AORs (but still operational control over the Atlantic)
Pacific Fleet Forces Command - training for deployments to 5th, 7th Fleet AORs (but still operational control over the eastern Pacific)
Basically, the Navy just sucks at coherent numbering, and finds decommissioning and commissioning easier than simply changing the role of a fleet.