To me, the most interesting thing about all of this is that civilian airports don't really have radar. You can disappear from an ATC screen just by turning off a transponder. If they'd had radar we would at least of known which way the plane went. A curious controller could have asked "unidentified object at height X, region Y" who they were and why they were in controlled airspace without a transponder on. The artic…
Radar is not exactly “new” technology, to your point I wonder why airports are not equipped with one. Shouldn’t break the bank. Plus don’t militaries have radar anyways for air defense? How is it possible that no radar from multiple countries picked up a silent Boeing 777 flying to nowhere?
Primary radar requires relatively a lot of power, and has other issues (e.g. target correlation) that make it of limited use for ATC purposes during enroute flight. If such radars exist, for military purposes for example, ATC may not have access to them as it's not really essential for their work. There are also large coverage gaps over oceans and in remote areas where nobody cares to monitor. These radars would only have a range of a couple hundred nm maximum, so they would not see deep into the Indian Ocean either.
So called 'over the horizon' radars also exist, but require truly massive amounts of power, not to mention capital to build, and also have very low spatial resolution. Apparently Australia's $1.8bn system was aimed in the wrong direction at the time of MH370's disappearance, or it might have had some low precision data to contribute.