I agree with the sentiment. But if you're a business owner, and someone says "we will make another 10-20-30 million dollars if we release for older systems".. Well, that's what you do.

I am a business owner and its not that simple. You have to take into account costs of developing and maintaining for ps3 and I suspect ps3 users are not the most profitable. Remember game sales are not the only income, I guess there are negotiations that involve playstation plus and console bundles. And being Destiny played five times as much as the second most played game, it will be in sony's best interest to have destiny 2 only for ps4. We will see, but my guess is that it we wont see it for ps3 xbox 360.

I know it's not that simple in reality. But you're also ignoring that this is big business. Not a small business/one owner kinda deal. There will be arguments from all over about development costs vs sales numbers. Activision (or whomever is going to front the cost) will want the biggest return, all other factors not withstanding.