But the big point of the entire Wargods arc is how the Wargods become less and less Ubuntu as time progresses. A more regular Ubuntu CO might have offered a surrender, but Kyrematen? Not really likely.
And even then, as Aesaar has pointed out, it is questionable if Admiral Leinonin had accepted it in any case. The Imperieuse had orders to inflict a killing blow on the Wargods; while having some of them surrender and others flee might have been an acceptable outcome here, it would also lessen the impact somewhat. The message Steele intended to send was probably "These are your best ships. I can wipe them out in a few seconds. Deal with it.", a message that would only come out garbled when a significant part of the Wargods is still alive at the end.
Not to mention that if you accept a surrender, you're obligated to care for them, run SAR, provide boarding crews, that sort of thing, all stuff that takes some time to execute, time that Imperieuse may not have (since she is sitting in a known location with a discharged jump drive).