It is way easier to remove something that is there that you don't want to use. Than to add something that is missing and that you want to use.
Here is a résumé of the situation.
Alignment in the game.
Me: No trouble using it.
Amount of work: none
You: God I hate that system. Let's put that junk on ignore mode.
Amount of work: none
Alignment out of the game.
You: Yes! Finally!. Thank God 6th edition.
Amount of work: none
Me: I want alignments in the game.
Amount of work: Must go over the 6ed MM all over and compare each monster and make annotations to each monster. Then, as new monsters are added to the game, I must read carefully each of them to pick what I would feel would be the "right" generic alignment. Then a new player enter the game and I need to explain all over again my stance. Even to other people just watching our Friday night D&D I will need to explain. Instead of a:" I decided to ignore a rule." I will have to explain every single decisions I ever made and even future ones will be debatable. Did I based my self on the 1ed MMs or later editions? And the next DM that decided to do the same thing as I? Did he based himself on an other edition?
So because you do not like something, you would impose on me (and other DMs) hours and hours of work, pondering and double and tripple checking where the only effort from your part, if alignments were kept would just be to put them on ignore? It is far easier to ignore something that is there than it is to redo from scratch something that has been removed.
You do not like alignment? Fine. Ignore them. Your table, your rule. But do not impose your choice on me. I considered alignment an essential part of what is D&D. It may not be as perfect as it could be for some, but for me, it works exactly as I want it to be. I do not impose a ton of work on you. Why would you impose that on me and others?