I'm not sure what hairline cracks you are referring to. If the cabinets have been built well enough and finished properly, you shouldn't get any hairline cracks in them.

It looks like where moldings are glued and when two pieces have been installed (for example the upper cabinets) the "seam" where they join...I've read a ton online and it seems fairly common with wood as it expands and contracts causing the paint to have some cracking. I just don't want to install and then two months later or even two years later have issues and I know this would bother me.

Those should be caulked and filled before painting.

Most painted cabinets won't be made of wood so they should contract like wood

We use soft maple or birch for paint grade cabinet door stiles and rails, The stiles, or horizontal pieces are coped (negative profile cut) into the vertical rails. The cope and stick joint (negative profile and positive profile) makes for the most gluing surface available. On shaker door styles this devolves into a simple tongue and groove joint. Wood movement is inevitable and small hairline cracks develop at all joints, glued or not. Wood used in cabinets should not split, this indicates that the moisture content of the wood was too high and the wood dried and changed shape and was not acceptable for cabinet construction. Caulking is not usually an option when factory finish is applied. Larger cabinet manufacturers and a lot of mid-level cabinet companies...and even small time cabinet makers...use white pre-catalyzed lacquer to spray on their products. It is hard and durable and resists stains and water (to a certain extent, it is a paint after all). But lacquer dissolves other paints and caulking..so the cabinets are not caulked or primed with a non-lacquer products. Wood movement is natural and so are hairline cracks.

Thermofoil, a thin layer of plastic molded over an MDF door or drawer was developed to eliminate the cracks in stile and rail construction...and to make it cheap. Thermofoil is cheap and you get what you pay for. Pretty much junk in my opinion. There was a debate recently regarding thermofoil doors...follow this link https://www.houzz.com/discussions/thermofoil-white-cabinets-what-do-you-think-dsvw-vd~267979