Maybe that person doesn't like to be touched. Maybe they had a past trauma. Maybe their arms are broken and hurt. Maybe they just think that hugging is in appropriate between two coworkers.

Their reasoning doesn't matter and they are under no obligation to tell you.

The fact that you want to decide it's ok for you to touch
somebody without their consent in ANY FUCKING WAY is the problem. You are not entitled to someone's else's body, affection or even attention. People don't owe you shit.