Let's look at three options. a, b and tenuki.
(Of course, if black is komaster, black could respond to white a with black c. But in general, black has to draw back to b because white will have little to lose in the ko.)
If Black does not play tenuki, he ends in gote. We can expect White a, Black b, White c in the late endgame.
(When compared with the sente diagram above, here is worth only about 9 points in gote. Before yose, this is relatively small, so tenuki is most likely a better option.)
Black gives up the possibility of tenuki and ends up in gote anyway. In the endgame we can expect Black a White b Black c.