This is just my own far-fetched hypothesis, but it might have to do with the upcoming WS terminator special squad, which is equipped with tartaros pattern armour. While it may seem contradictory, my guess is that FW is releasing the praetor in a different pattern to the special unit so that, should you want an HQ with either pattern of terminator armour, you can get it from them through the single praetor or the terminator unit. The same has happened with the Blood Angels praetor and special terminator unit.
I like everything about both models, save one major detail: why is the Terminator Praetor in Cataphractii instead of Tartaros? wouldn't that make more sense for the Scars speed focus?
I'm not saying that this the real reason nor that it would actually be a good idea from FW, as having the praetor and the unit in the same pattern would probably be an easier way to sell them together, and the AL release had matching armour patterns, if I recall correctly. Maybe it was just a matter of the WS sculptor wanting to sculpt both patterns .
Edited by Elzender, 07 April 2019 - 08:40 AM.