I think the point is that there will always be those who favor witnesses who run their own boxes and do not outsource this important aspect of the job to a company that also hosts other witness boxes, because the mere attitude towards this being okay makes the blockchain vulnerable and overly centralized in case there are any malicious hacks, ddos attacks, or state-level action taken against the company. It's not so much that privex or any other hosting service are bad in and of themselves, but rather that a main selling point of dpos and multiple witnesses is to at least maintain some level of decentralization and resistance to attacks on the network that are only made easier by putting all of your eggs in one basket.

If all 20 top witnesses use one company that runs boxes out of seven continents, it still won't matter how geographically dispersed that company's hosting services are if, for example, a nation has the ability and authority to confiscate all of that company's servers in one fell swoop.