Attackers have the element of surprise. Unless you are part of a group yourself, you cannot hope to have enough people to keep a sufficient watch. The isolated 'living off the land' types with big stockpiles of supplies would be easy targets.
You have to sleep. You have to get water and maintain certain other things outside your home from time to time. You may get sick and need additional rest. Or to go and get firewood etc.
If 10 people really really want your food and supplies, they will burn you out or crash a vehicle into your home, or drop a tree on it. Alone you are nothing, you are much more in a community.
Think minute men vs a lone wolf. It is no contest.
Build a better home, learning from the story Three Little Pigs. Don't build from straw or sticks.
See https://www.monolithic.org/ for the right way to build. Crashing a vehicle does nothing. One of those homes, at the bottom of a hill, withstood a run-away 18-wheeler with only cosmetic damage. Fire could damage a layer of insulation, but only if the dome isn't covered in stucco or better. Get the impact-resistant windows plus shutters, and get the tornado-resistant door.
Robbers will choose the easyiest route. They just want stuff and not assasinate specifically someone, they will rob somebody other if they find a hard target. Probably somebody like you. It works the same with muggings. 2 people is enough to get some sleep and run errands.
The thing is, bad guys have guns too. You can't really defend against many thugs if they take you by surprise. Somebody could just wait somewhere near you house and snipe you, it's impossible to detect everything all the time if you leave your house or go near windows even once. And bad guys can use even explosives to break into your house.
Don't get me wrong though, since guns are extremely useful for defense and most of the bad guys aren't very tough. Surviving without a community in a serious scenario is just impossible.
How often are those preppers actually trained to take on several armed attackers?
It's not often. Having ten firearms and a million bullets doesn't help you much if you're a semi-crazed loner who vastly overestimates your abilities and usefullness