Probably due to time / resource constraints. Many popular bikes like the Trek SC, Felt IA, Cervelo P3 series weren't included, either.
This wasn't a for-profit test by a trade magazine. Testing of Cervelo P5(x) are possible because of generous help from a bike shop and gofundme donations. Testing of Tactical were provided by the manufacturer. Tunnel time was paid for by gofundme.
The Felt B series represents an aero optimized entry bike. Cervelo P5-6 represents the peak of past gen bikes. P5-X, Ventum, and Andean are the cutting edge shapes, for which we have seen limited aero data on. Tactical represents a "value" alternative to $10k bikes.
An aero optimized Shiv would probably fall in the middle of the pack. We are talking about no more than a 10 watt difference between the fastest and slowest bike here.
Does anybody knows why the Shiv wasn't included in the aero shootout? It seems to be one of the more popular frames out there.