Apparently the booster signaled it didn't have enough fuel to risk it. Either because it consumed more then expected on the way up, or a measurement error potentially.

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Laremere 3 hours ago | parent | next [-]

At the last moment the exhaust turned green. That's consistent with the fuel running out, the engines running oxygen rich, and subsequently "engine rich". So I would put my money on actually running out vs a measurement error.

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bavell 3 hours ago | parent | prev [-]

I heard somewhere the engine efficiency is still somewhat variable so they burned more fuel than anticipated.

	▲	quotemstr 3 hours ago \| parent [-]
		That's basically what Musk said, yes: that they need to work on both engine performance and performance consistency. He said they'd be cutting off the main engines one second sooner to provide more margin for boost-back. Amazing that a one-second difference can matter, but those things go through tons of fuel every one of those seconds!