[Azred]

1. Because the plot called for it.
2. Because the plot called for it.
3. Because the plot called for it.
4. Because the plot called for it.
5. Because the plot called for it.

It is meant to be an entertaining movie, not an after-the-fact analysis of a successful military campaign.

However, just to be fair....

1. It's amazing what you can do with real-time interstellar communications these days. He called ahead.

2. He was otherwise occupied at the time. Besides, Dooku could have countered Yoda's influence.

3. To put a more controllable Senator in her place.

4. What makes you think he didn't know about it? Rest assured that he has been paying close attention to the Senatorial goings-on.

5. Yoda himself says that the Dark Side is difficult to see, even for the Council.