Continuity mistake: During the opening briefing with Palpatine, Mace Windu and Yoda, Luminara Unduli attends via hologram. But during the shots where Obi-Wan is explaining the attack plan, and the shot over the shoulder of Palpatine's hologram looking at Obi-Wan and Ki-Adi-Mundi, Luminara is shown as being physically present (i.e. not a blue, translucent hologram). After Palpatine, Mace and Yoda sign off, she's back to being a hologram. (00:02:00 - 00:02:30)
Other mistake: Commander Jet does not hold the rank of "Captain", but he's addressed as such, just as many times as he's called by his proper rank.
Answer: I guess that 1) the King assumed that Ventress' droids were meant to capture the Jedi, not kill him outright. When she yells at OOM-224 to shoot Yoda, she evidently failed that expectation. 2) Sending out a bunch of Droidekas after it is plain that Master Yoda has clearly won is not a sign of good sportsmanship, either.