There is really no need to bring this topic up again when there have been numerous threads on the subject, many with replies from us.
We are aware that some players wish for the game to have closed servers, and in a perfect world that would be the case.
It has always comes down to the initial cost of retrofitting the entire engine to support it, future maintenance costs of such a service and (which is frequently not considered by players) the cost of opportunity (aka the time we spend on this is time we cannot spend on other things such as expansion(s) or future products).
The fact is, about 10% of ARPG players even touch MP (this data is consistent throughout history of ARPGs and remains consistent with Grim Dawn). Just because people have to go online (as with Diablo 3 and Path of Exile) to play does not automatically make them want to share that experience with others.
In the end though, for us, it falls to finances and focusing our resources where they best benefit our audience.