But you should note that Cruz built that organization in Iowa over months and gave speeches in every Iowa county, multiple times, over months leading up to the caucus, being the only candidate to give Iowa nearly that much attention. He doesn't have that kind of time now.
Giving speeches is campaigning, not organization. The organization consists of his people there doing outreach to voters to get them to show up on caucus day. That's been going on for weeks/months, and doesn't require his physical presence in the state. (Though he is also spending more time than any of the other candidates campaigning there during this three day window between SC and NV.)