> Understanding what happened, and potentially making a few improvements to plane safety as a result.

Well Wikipedia says a Boeing 777-200ER costs $261.5 million[1]. That's about double the cost for the search. If it's possible to prevent even one future mishap as a result of learning anything the cost is justified.

Besides closure is important for the families and friends of the passengers. Especially with crazy articles saying the plane could have landed in Kazakhstan[2]. Imagine the suffering people must be going through thinking their loved ones are 95% dead but 5% possibly maybe caught up in a crazy conspiracy. Even if it's 1% or 0.001% likely it could be enough to keep one awake at night.

[1] https://en.wikipedia.org/wiki/Boeing_777 [2] http://nymag.com/daily/intelligencer/2015/02/jeff-wise-mh370...