That's the point, of course.
But see, that's why so many people disliked the trilogy: the plot was good but the execution was so awful.
It would have been better if there were a reason that the senate couldn't get along.
Having characters just be stupid is not good storytelling.
I call this the "great sin of storytelling": when you make a character do something inexplicably dumb just to create conflict so your story can continue.
Lots of movies and TV shows do it. ::shrugs::
I think Rogue One did a reasonable job. The rebellion didn't want to try to steal the plans because they didn't want to risk open conflict.
That's an understandable reason.