There are no other issues. It's plain lack of mindfulness/care and greed.

Back in the old days, almost every multiplayer game had a LAN mode and many games came the server software to host a dedicated server on your pc or anywhere else.

Keep in mind game budgets were far smaller back then and not 100+ million affairs. There's simply no excuse.

Ok, well gee - this could fall into and have TWO different problems/issues.

#1 is the removal of the publishers servers render the software unusable?

Sadly this seems to happen all the time as publishers take down 'key servers' that are/were required to unlock their software titles. While the publishers argue that users ought to purchase a new version of the software that IS supported good luck unlocking MS Office 1997 or WIN2000 anytime soon. (for example) :)

#2 while #1 above would/could cover an 'online only' game, many titles have a 'multiplayer' add-on or extra mode for online play that is apart from the 'single player mode'.

I'd agree that it could be a 'grey area' however I doubt that companies would ever be required to support any given release FOREVER if they are not currently selling it.
However just like with #1 above *if* they are no longer selling it they ought to provide a means for the user/purchaser to unlock and/or use the software by some other means.

For online games or games with an online mode this would be releasing the server side software for those that would like to host their own games. Packages requiring a 'ping' of a 'license server' there ought to be a tool that disables that requirement.

It surely could be a nightmare as software does not 'wear out', degrade or self destruct like physical items might do.