Any Biology majors here?
Why would these ancient viruses be more genetically complex than modern day ones, like the Influenza strain?
Perhaps they can learn something from it and use that knowledge to work on cures for modern illnesses.
Other than that, it's probably morbid curiosity lol
The extra genes are for doing the total conversions on cells, turning bodies into bacteria factories which eventually explode to spread airborne during phase 1 of the invasion.
Not a biology student, but I'd expect that viruses become smaller over time as any genes which aren't absolutely necessary for propagation get filtered out