How was Prince Ptolemy’s citizenship rejected??
Player support is a very important factor, but not the sole one.
At this point in history Roman citizenship is still highly priced, to the point in which 40 years ago Rome had to go to war against Italians demanding citizenship, and not even the people of Cisalpine Gaul were granted citizenship until Julius Caesar (in what already was a controversial act). To grant citizenship to the likely heir of a foreign throne (amidst rumors that he might marry inside a Roman family) of a Kingdom so questioned as Egypt in this time period would be offensive and unacceptable to many Senators.
Cato successfully seized on that on what I judged to be an able peformance, and so I ruled it likely that most of the Senate would rather reject the proposal (after alarms were set at the percieved to be dangerous notion of Pompeius marrying into foreign royalty) than accept it.
As you see, the Senate can be fluid and a player can manage to surpass other players in the Senate, but it requires a "perfect storm" so to speak. This seems like the case for me.