Because their stupid, narcissistic, blinded by greed, and constantly believes...
But that's the thing I don't understand. If a company is "blinded by greed" why jump into a game genre where the majority of the games have failed, and the ones that haven't failed didn't actually make all that much money.
I understand companies looking at Call of Duty making a billion dollars per game and going "I want to get a piece of that" and then making call of duty clones. After all, a call of duty clone is a short 5 hour game that's easy enough to churn out, and an unsuccessful one isn't going to ruin a company.
A Destiny clone is immediately a risky proposition because the most successful one was still only moderately successful, when you make one you have to make TONS of content for people to not burn through it instantly, and you're tied to years of upkeep even if the game isn't successful. It just seems like a bad investment all around for a "greedy" company.
Like I said, if Destiny had been a goldmine Activision would still be holding onto it. They literally just gave it back to Bungie because they didn't want to deal with how much resources it took to run versus the return they were getting. What greedy company looks at that and goes "I need me a piece of that headache."
The only other successful version of this model is Warframe, and that's not exactly a huge cash cow either. It's a good successful free to play game, but it doesn't exactly print money on the scale all of these companies seem to expect. I'm just not sure where this expectation of making "all the money" comes from.