If you look at the blocks before your txn was included:

HeightTimeMinerElapsed# tx% new (?)Block ValueTotal FeesSizeFee/size (?)
392,1501h 15m ago - 07-Jan 20:05F2Pool12m 22s247651%14,513.683964990.40601258999,999 B40.6012986
392,1491h 27m ago - 07-Jan 19:53BTCChina31m 45s227797%22,482.465414900.56340120949,030 B59.3660
392,1481h 59m ago - 07-Jan 19:21Slush11m 58s168178%29,171.164376750.29257031749,158 B39.0532184
392,1472h 11m ago - 07-Jan 19:09AntPool14m 06s178390%16,789.758356120.36324329933,337 B38.91877
392,1462h 25m ago - 07-Jan 18:55AntPool2m 14s18954%12,945.036017510.25293064931,463 B27.1541263
392,1452h 27m ago - 07-Jan 18:52F2Pool23m 38s308377%26,494.591148470.61388991999,961 B61.3913852

It was basically a case of bad luck in that blocks were being found slower than 10 minutes, causing a backlog.
If you look at the last portion (BXXXXX), your fees/byte were lower than all the others that got included, so miners picked more urgent transactions instead of yours.