An interesting question and one with many answers, to a large extent it comes down to costs and reliability.
Winch motors are DC electrical motor powered, this means they have two wires to power them, in a single solenoid type it will have a central off position, once it is powered one way it will basically rock one way and connect both the positive and negative feeds through two sets of contacts internally, lets assume this is power out. If it is powered the other way, power in, the solenoid rocks the other way and connects two more sets of contacts, these are cross linked internally so the positive and negative contacts are the opposite way round and the motor goes in reverse.
These one piece rocking types are built for cheapness and not reliability and it you get a problem you are stuck.
With four individual solenoids you have a single acting solenoid, its either open and not working or closed and making contact and the winch is running, basically they only work on one plane and its only function is to open or close the contacts of an individual wire.
Four solenoid models are flexible and reliable, if you have an issue winching in or out and you have a solenoid fault you identify the faulty unit and swap it for one of the others, most of the time you will use a winch for pulling and you can set it to freewheel for pulling rope out manually, so getting you out of the mire.