Keep in mind that the IIci was still in the lineup when the IIvx was introduced and would be for a few more months. It may have been a marketing decision.

I'm more interested to know why the IIvi was introduced. It was never sold in the US; perhaps it was intended for markets where a "stepping stone" between the LCII and the higher end Macs, including the IIvx, was needed due to trends of the day? It seems to have identical specifications to the LCII except that a 68882 was available as an option.