There are several things you mention here so I'm kind of confused what to answer.
First, tacked on MP. Consumers don't know what they want, so if they want MP on a game that shouldn't have it (see Mass Effect 3) developers shouldn't put it on there, it is not only a waste of time and money but it means they spent time developing some crappy MP which can take away from the single player experience. Infact with ME3 they made it worse by having it affect the story, "Didn't pay for Xbox Gold? then screw you, you aren't allowed to get the full experience of the single player game you paid for." is basically what they said here.
Second, single player that require a connection is a joke. Sorry it is. Destiny has lost it's sale from me. No net connection means you can't play. And people wonder why we all moaned at MS for their DRM crap, online only connection for a single player game IS DRM.
Third, Multiplayer games that are advertised as such and are only MP games, shouldn't be full price especially when you have to pay more to play it on consoles. It's no different to a MMO subscription which is becoming increasingly obsolete. If their servers vanish, that game is useless so any more ever spent on it is pointless and a waste.
these are my current thoughts, I have many on the way industry is screwing us.
Hmm, pie.
