Good grief - they searched where they did because they (thought they had) detected ULB pings. Even if the pings didn't turn out to be from MH370, it would have been pretty stupid to have swanned off to the Inmarsat "most probable" location, while meanwhile the ULB batteries would have died in a "less probable" location.
This hindsight-enhanced armchair second-guessing of a very professional search team gets a bit ridiculous at times.