We chose the Super Hornet has a bridging or temporary strike capability to replace our rather old and tired F-111's until the F-35 Lightning II - Joint Strike Fighter is available to fulfill our tactical fighter needs. The Super Hornet is expected to serve from 13-15 years in RAAF service, with no decision yet taken (publicly known) on what will happen to them in the 2023-2025 timeframe.
The Hornet and Super Hornet are carrier capable aircraft. That doesn't mean they can't fly from land bases as well.
Canada, Spain, Finland, Switzerland, Kuwait and Malaysia also use the F/A-18A/B/C/D in a land based role and chose it for reasons other than it's ability to take off and land on aircraft carriers.
Further addition, the F/A-18F Super Hornets were selected as the bridging aircraft due to an urgent need to retire the F-111's from service. IIRC the F-111's were originally expected to be kept in service until ~2020, but due to some issues with the airframes (wheel up landing IIRC) as well as the exploding cost to maintain an orphan legacy aircraft and the increasing irrelevance of the capability in the face of modern air defence threats... The decision was made to retire the F-111 in 2010.
Once it was realised when the F-111 would be out of service, it was know that the F-35 would not be ready for service by then, so the RAAF would have a gap in terms of strike capability. The only aircraft the RAAF could get and actually reach IOC with to cover part of that gap, was the F/A-18 Super Hornet.
The RAAF could have placed an order for some other fighter, like the Rafale, F-15 or F-16, but by the time the first aircraft was delivered, it would likely be about the same time the RAAF would start taking deliveries of non-LRIP F-35's.
There were several reasons why the RAAF could get an order for F/A-18 SHornets into service sooner than other fighters. Amongst them was that the USN already had a contract for SHornets which Boeing has been producing, and the USN was willing to allow the RAAF order to 'jump' USN production slots. This means that aircraft which are being built at a steady rate (4 per month?) would be ready for delivery sooner than if production needed to be re-started or ramped up. By comparison, the Rafale is being produced by Dassault for the French Air Force and Navy, but Dassault is AFAIK only producing ~11 Rafales per year. In the case of any order for the F-15 or F-16, it would have required the RAAF to wait until deliveries were met for existing orders, unless the nations/services awaiting such orders could be induced to delay receiving their aircraft to allow the RAAF order to 'jump ahead' in the production queue. Then there would also be the need to setup the various support functions which are required for the RAAF to operate new aircraft types.
Also, while the F/A-18F looks very similar to the 'Classic' Hornets in RAAF service, they are entirely new fighters. Having said that, the two aircraft are very similar, so pilots of the Hornets can be quickly transitioned to Super Hornets in a matter of hours. This means that while the SHornets are a new type for the RAAF, including this fighter into the mix of aircraft has been easier than if the design was not already so much like the older Hornets.
-Cheers