They're the only thing involved pretty much. The gulf nations have not allowed the US to launch from their bases in the region. Maybe that will change as they keep getting attacked but as of now the carriers (and now the base on Cyprus) are where the planes are coming from. The strategic bombers, prior to Cyprus, were taking off from the US and flying all the way to Iran and back.

> The gulf nations have not allowed the US to launch from their bases in the region.

This is a categorically false assertion that they have been putting to assuage their local populations - which are heavily opposed to the war and the US support. Maybe not all of them, but some of them, like the UAE and Saudi Arabia, are clearly hosting and allowing the US to prosecute the war from their soil. If they weren't, you wouldn't have had the AWACS aircraft getting turned to smithereens in Riyadh.