Malaysian Airlines MH370 contact lost

[Shadoko]

So why did they?

IMHO, an erroneous detection by the HMS Tireless (remember the "self satisfied" statement when she returned to England?) and then, using the pinger locator of the Navy towed by Ocean Shield at the limits of its capabilities, a "false" signal from the black box pingers.
Anyway, it was (IMHO) the right thing to do if there was the smallest chance to find the plane there.
Perhaps this can't be told for "military" reasons (Tireless capacities) and thus the Australian can't tell that, nor show the "signal" acquisition charts (Navy capacities). Nothing abnormal from my point of view this is not made public. And they don't lie: the search zone was moved after "more study".