If my dog doesn't say hi on walks is that bad?
Not at all! Dogs are very social animals however they are also individuals. Not all dogs want to/need to meet on walks and there can be many reasons why.
Shy dogs will benefit a lot from being able to maintain distance and be allowed to slowly approach, at their own comfort. Reactive dogs need more training support but not being allowed to meet if the setup isn't ideal will prevent an unwanted scenario from taking place.
Overly excited dogs may benefit more from an open (safe & controlled) environment where they can let their energy out first, before being expected to meet or not meet other dogs on walks calmly.