Sociability is a spectrum containing degrees of social behavior. A small percentage of dogs lie on one end of the spectrum. In general, they are reactive, aggressive, shy etc. to other dogs or people. If this is your dog, you are not alone. This can be improved through training.
And an equally small percentage of dogs lie on the opposite end of the spectrum. They are social butterflies, and they love everyone and anyone, and they are not overly excited, causing them to bark, jump and misbehave. You see these dogs EVERYWHERE because they CAN HANDLE going everywhere.
But the vast majority of dogs are like you. They generally get along well with most dogs and people but not all dogs and people. This is a normal, and it is a reasonable expectation for your dog.
What to do when sociability gets worse
You might have a dog whose sociability is getting worse. This is also normal! Because behavior is always changing. It is either getting better or getting worse. It is not stagnant! Training helps your dog improve its social behavior, and it helps you maintain its present sociability. So how do you do that? You team up things your dog likes with dogs and people at a distance your dog can remain calm and confident.