Answer:
The reason he was concerned about standing is because it's a formal thing to do.
Step-by-step explanation:
Standing at speeches and presidential debates or even in conversation is an important aspect to earning and giving respect. By sitting Roosevelt would have been looked at in an aspect that would have been negative for him. Presidents today would most likely feel the same. My reasoning behind this is that they need to gain respect and trust from their voters and supporters.
I hope you can benefit from this. :)
-AidanGregLyons