The flaw in your thinking lies in supposing that bicyclists are members of some sort of group that either welcomes people in or rejects them as outsiders.
If you just consider them as people, you're open to all kinds of other reasons why they may not return a greeting. One may simply be that they're too focused on their endeavors at the moment.
Walkers tend to be more open to greeting people because walking is slower paced, and rather than needing focus, invites distraction to fill the time.
My advice, stop worrying about others, and be your own person, greeting or not greeting as the mood strikes you.
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WARNING, I'm from New York. Thin skinned people should maintain safe distance.