the right side biker seems to be reluctant to get off from his bike
is it a rule or something?
Human behavorial instinct.
Firstly, people are resistant to changes. We also tend to be as efficient (ie lazy) as possible. If I can pass the ketchup across the table while seated, I will not stand up to do so.
Secondly, he instinctively know standing up means commiting to a decision to do something more drastic. Such as deciding to fight.
Thirdly, the instinct to get out of danger as quickly as possible. Staying on the bike means can run away quickly. Getting off means giving up this advantage.
Somewhere in his subconcious, there's also a possible consideration that if he gets off, some stranger might take advantage and ride away quickly with his bike
Reasonable possibilities?