The latter iis probably the main reason. As you apparently have a good knowledge of Marine operations a great deal of the ops take place from ships and the aircraft would need rigged with some type of AC landing mod. But I must say this the Army rid themselves of the LAV-25 and not only do the Marines use it but they improved it and it was essential in the 1st and 2nd Gulf Wars!!!!! I LOVE MY UNIT 3rd LAR BABY!!!!
Most folks don't realize that ALL Marine pilots go through the Basic Infantry Course, and then spend a year deployed with troops on the ground asa FAC before they go off to aviation units...It gives them a very different perspective of what the grunts go through, and also what the mission of "supporting the troops" REALLY is all about....and what the "close" in close air support really is all about....it means something special when the the officer on the ground talking to the pilot knows that the pilot has been in his position, and visa-versa...
The A-10 flies slow enouigh that it could probably take off from a carrier without a cat..though modifying it wouldn't be too much of a problem..neither would adding a tail hook..and you'd probably only need minor beefing up of the landong gear...heck.it probably lands at 70-80 mph...and with 35 knots over the deck...that's a net 40 mph llanding speed....easy.....I think, upon reflecting, that the reason the my Marines didn't push for the A-10 when it was in development was thatbat the time they were pushing for the Harrier....remember..that's the FIRST and only time the Corps got its own aircraft...and the mission/profiles of the two planes were pretty similar, and the Harriers are faster, and can land/take-off from the assault ships...which lets them operate as part of a self-contained MEU...