Its optional so people can choose what they want to do. Almost everyone likes to choose for themselves instead of being forced against their will to do something they might not want to do. Almost everyone prefers to be given a choice. Your question seems to do nothing but to find fault with something that most people prefer (getting a choice). Almost no one ever complains about being given a choice. Of course there are exceptions to every rule as your post illustrates.
If you want a new phone would you prefer to be able to chose the phone you wanted or would you rather be forced to buy a particular phone against your will? I think most normal people would rather have the choice to chose for them selves. See, its that simple. I'm actually surprised that anyone would even ask this question if they just sat down for 5 seconds to think aboout it.
And... if it were mandatory even more people would be complaining about it. I really shouldn't have to explain this either as long as you read what I already wrote