Oliver Bud,
For a new shooter, the existence of so many calibers is an opportunity, not a problem. It means you can find a Ruger American Gen II that is specifically suited to your needs and comfort level.
Having around 8 - 12 diff calibers for a rifle like the Ruger American Generation II is common in the firearms industry. This variety allows customization for different purposes such as hunting small game, medium-sized game, or target shooting by offering specific performance traits like recoil, trajectory, and power. Smaller calibers (.204 Ruger, .223) are ideal for varmint hunting and target practice, with low recoil. Medium calibers (.308 Win, 6.5 Creedmoor) suit deer and long-range shooting, balancing recoil and accuracy. Larger calibers (.300 Win. Mag.) are for big game like elk. Manufacturers provide diverse options to meet market demand and personal preferences. Enthusiasts see this variety as a benefit, offering specialized tools for different needs, and enjoy the research and selection process, fostering a culture of learning and experimentation.

Hi Oliver and welcome. This is two-fold. Manufacturers usually make the same firearm in the most popular calibers. This affords shooters the ability to select their preferred caliber and it also gives the manufacturer more overall sales. Not many car manufacturer with one vehicle with one motor or trim option. In short, catering to the masses. Cheers, stay safe and enjoy!

Different calibers for different purposes. Everyone need and desire is different.

Why so many calibers?
Diverse Shooting Needs: Different calibers are suited for different purposes. A .223 Remington is ideal for small pests, while a 6.5 PRC is excellent for longer-range hunting of larger game.
Popularity and Demand: Ruger offers calibers like the 6.5 Creedmoor and .308 Winchester, which are among the most popular and widely used for hunting and sport shooting.
Newer Caliber Options: The Gen II lineup includes newer cartridges such as 6mm ARC and 7mm PRC, giving shooters access to modern ballistic performance.
User Preference: Shooters have different preferences for recoil, trajectory, and the type of game they intend to shoot, and having many calibers allows them to choose the rifle that best fits their shooting style and needs.
How do enthusiasts feel about it?
Positive Reception: Many gun enthusiasts see this as a positive aspect of the rifle, appreciating the versatility and options it provides.
Versatility: The wide range of calibers makes the Ruger American Gen II a very versatile platform that can be adapted to many different roles, from hunting to recreational shooting.
Appeals to a Broad Market: The availability of multiple calibers helps the rifle appeal to a broader audience of shooters and hunters who may have different skill levels and target applications.

Oliver Sir,
I think I know where you're coming from. Very similar as to why phones are always being updated or why cars keep coming out with new colors and different models etc? Having approximately eight different types of calibers for the Ruger American Generation II is not just a marketing strategy, but a necessity based on different shooting applications and shooter preferences. A single, universal cartridge cannot perform every task equally well, so different calibers are developed to offer a range of characteristics like recoil, power, and range.
For a beginner, the large number of calibers isn't meant to make you buy multiple guns, but rather to ensure there is a perfect match for your specific needs, whether that's low recoil, a particular hunting application, or affordability.
Hope the above info helps Oliver Sir and please take your time searching for the right one specific to your needs.
Take care 🙏🏻

Well ask yourself what are you going after. Deer then 30 caliber and less . Elk you need upper 30 caliber. 300 Winchester to 338 375.

Having a choice s a good thing. What you are going to do with the rifle helps narrow down which caliber you want. If hunting, type of game narrows it down more. Have fun with it, and get feedback from people you know.

There are actually between 11 and 18 caliber options depending on the model. But the answer is the same for all firearms, they are offered in many options because they sell. For the actual differences, factors are ammo availability and cost, different game sizes requiring different types of rounds, effective range and trajectory of different ammo, recoil tolerance of the shooter, sometimes regional hunting rules, and also just familiarity/preference to specific cartridges that some have been shooting for decades.
Personally, I have the American Gen II Ranch in .223 just because I like plinking at targets for relatively low ammo cost and am not interested in hunting.