You will find a ton of unused, unusable and partially used stuff collecting cobwebs in the tack room of any horse owner who has been at it for a long time. I know of a lot of people who have a lot more bits than horses.
Take a look at the catalogue of any tack dealer, and you will see whole section on bits: English bits, Western bits and bits of types you simply will not recognize. Some of the bits on sale are endorsed by well known personalities in the world of horses who presumably developed those bits, use them or are paid to make you think so. A lot of keen horse people rush to buy bits endorsed by their favourite idol.
There are any number of reasons for the large collections of bits stores carry, some of them attributable to horses and some to riders. Even if you are fond of just one type of bit, you will find a large variety of derivative bits. Bits are made of various material and come in plenty of styles and sizes. They also come with plenty of mouthpiece options. I had a mentor a few years back who once remarked to me that she was not very fond of aluminium bits, but still kept a few of them handy because every now and then she would run into a horse who seemed to prefer only aluminium bits. She was smart enough to know when to let these horses have their own way on minor issues; on major issues she made the decisions. The arrangement usually worked fine for her and her horses.
People who are into showing keep a big variety of bits. For each discipline they participate in, they use the appropriate bit. Within each discipline, too, they use different bits for different horses, English pleasure riding bits are much different from bits in classes to do with the hunt seat, while bits for western pleasure riding involve an entirely different type of bit. Finally, within each type and sub-type of bit, there are bits of various sizes and material and mouthpiece types.
I find that people who have problems with horses tend to keep on accumulating bits because they are busy getting a new one every few days for the horse. They believe the solution to a recalcitrant horse is a harsher bit. You will find bits of all sizes and types (mild to very severe) in the barns of people like this. You may find some rather questionable bits like those with twisted wire, those with chain mouthpieces, or those with longer mouthpieces. Such a collection would not speak well for the horse owners concerned, who obviously believe in cruel bits being the cure for their recalcitrant horses. These people have neither the patience nor the inclination to get professional help with their horses.
A horse person’s bit collection can tell a lot of stories about that person. In specific, the collection tells stories about the person’s horsemanship. You will find horse owners whose collections consist of easy shanked bits with mouthpieces as light as feathers, and you will find horse owners who seem to believe pain brings out the best in horses.
If I were in the market for a horse, I have absolutely no doubt about which horse owner I would give my custom to.