I think Ric is fond of saying "would have" is a guess mascarading as fact. #2 and #3. Did they have enough energy to do an SOS by the time it became apparent that rescue wasn't coming right away? Were they even expecting an air rescue at all? By the time they were nearly dead, would they have prioritized building a bunch of rocks to mark their presence, or finding food and water? If they had left some kind of a marker, would it even have been recognized as such? What you think they would have done are not in any way "no brainers" in the situation they were in. I don't think the fact that they seemingly didn't do any of these things is much to discount the Niku hypothesis.
I think the first point, though, is a really good one. Why in the dickens didn't Fred Noonan transmit their location? Possible answers that have been suggested by the available evidence at hand are, if I recall correctly:
1. They didn't know exactly where they were, possibly because the shape of the island did not match what was on the maps they had at their disposal, and did not want to misdirect the search effort by giving the wrong island name.
2. Fred may have been incapacitated and unable to do the necessary navigational readings.
3. They did try to transmit their location, but none of those signals were ever picked up. (Most of the post-loss messages are fragmentary, garbled or non-existent [e.g. carrier waves or indistinguishable voice]. The only lengthy message that exists is Betty's Notebook, and that is fragmentary and filled with numbers and letters that may have been garbled attempts to transmit that information -- numbers that are one degree off the line of position they last flew recur several times in the notes, as do the words "New York" or "New York City" which may have been a mishearing of "Norwich City," the shipwreck the plane may have landed near and the most identifiable landmark nearby)
I do feel you on this last point, because even though in the main I'm convinced by TIGHAR's circumstantial case, I do have a problem with the idea that Fred Noonan was too incapacitated to figure out where they were but he was still OK enough to man the radio a night or two later. I can construct a plausible scenario where that's how it went down, but it troubles me a bit.