There is no "major difference". Both programs follow a different philosophy which makes them have lots of differences. SolidWorks looks more modern and focuses on user-friendly operation and is somehow limited to what it shows you, CATIA acutally is the opposite, making it more hard to use but is not limited in what you want to do with it.
It depends on what kind of things you want to do to select the proper program, most small machine things can actually done with both.
Thre Price is not that much different by the way, they both have cheap licences for basic functions and higher prices for the fancy stuff. Most people shout things on the internet which they read there but after contacting sales you'll see theres not much difference.
solidworks is superior for the part modeling and the CATIA is more superior for the surface work
Price (money) and volume of job.