Because my bikes do different things. Most of my bikes are commuter ready with racks and lights (although the lights are coming off as I get closer to retirement). I have a touring bike that I use for road touring. I don’t usually ride it for a lot of other riding, however. I have a cyclocross bike that is my main commuting bike...and has the most mileage of any bike I’ve ever owned...that gets use for a lot of general riding as well. I have 3+ mountain bikes (more on that later) that I use for various things from commuting to general riding to bike packing. The bikepacking bike is a Moots YBB that has a little bit of rear suspension which is enough to take off the edge but it’s not a long travel dual mountain bike. one of the “mountain bikes” is actually a cruiser that I use when I ride with my wife as it has similar gearing so that I don’t outrun her (as much).
All of these bikes have racks so that I can carry stuff to work or where I can carry stuff during winter rides.
I also have a go fast bike that really doesn’t get ridden all that much because it’s for going fast and not carrying anything. It’s not a good bike for winter...the widest tires it will take are 25mm slicks. I also wouldn’t want to put a rack on it since it is not designed for that.
The “+” mountain bikes are 2 dual suspension mountain bikes. Both are Specialized S-Work Epics...the best dual suspension system ever made in my opinion. One is at my home and I use it occasionally but it’s a bit like the fast road bike...no racks for carrying anything but me. The other is at my daughter’s house in Arizona. I have that one down there so that I can ride on roads and paths...the front and rear suspension are (or can be made) rigid...or for real mountain biking where the suspension shines. I could probably use the one at home for bikepacking but it would be very limited on what it could carry.
If push came to shove, I could probably get rid of the cyclocross, the go fast bike, maybe 3 of the 5 mountain bikes and be perfectly happy. But what’s the fun in that?