True. It is technically possible to create a "stack" of LEM appliances for different roles, so flow could be one of those roles, if the use cases matured.
The other honest side to that coin is that after deploying the top talkers functionality, we didn't see a lot of customers who were at the point where they were ready to see security value from flow data - they could barely keep on top of their log data. Regardless of whether it was within LEM or NTA, it would behoove us (them) to SolarWinds-ify the use cases