I could be in error, but, it seems that the Senate and the masses have different interests. The Senate likes that you complete their missions. The masses appreciate victories and conquests.

Signing a cease fire can cause loss of popularity with the masses. Stunning victories boost the masses' admiration while making the Senate more wary of you.

When the time comes, it's the masses that urge you to take Rome, due to your popularity, not the Senate.

It's please one or the other, it seems, not both.