The series might not be popular but Daizyujin could be. If they like the design they will buy it even if they do not like the show. Though most likely they are just jumping on the band wagon of giving us more Mighty Morphin Crap for the delight of some and the annoyance of others.

Golion wasn't particularly popular in Japan either. Most likely it was made into the SoC line to appeal to western markets who know it as Voltron.

I do think GoLion and DaiZyuJin SoC were made to expose the line to a broader western audience. I wouldn't be too suprised if we get a Soul of Chogokin Muteki Shogun or Ohranger Robo. That makes me fear that we might not get any pre-Zyuranger SoC besides what we already got: Battle Fever Robo. I heard a SoC Sun Vulcan Robo proto-type was made but never entered production. If they want to pander to Europe they might release BioRobo.

Here is a list of what I think are likely to get made:
1) Sun Vulcan Robo (if it's true the proto-type exist)
2) BioRobo
3) Live Robo
4) Muteki Shogun
5) Ohranger Robo
6) Dragoncaesar
7) DairenOh
8) GokaiOh

List of SoC Sentai Mechs I'd like to have made:
All of them