And where would that be? Why is it harder to cut the cost of a limo, or flowers, or alcohol, or a honeymoon, or your dress, or your ring, or the meal, or the music, or the invitations, etc.? Yes, I'm being facetious. I know exactly why it's harder to cut those.
Because the bride and/or groom want them. That's the bottom line. The bridge and groom are willing to cut things they don't care about, but not the things they want. And hey, that's human. I have no problem cutting the favors out altogether. I simply have an issue with announcing that you have done so that you can
Do Good And Make Sure Everyone Knows It, But At No Cost to Yourself.. Well, if your guests are entitled to favors, making a big deal about leaving those out so you can
Do Good And Make Sure Everyone Knows It, But At No Cost to Yourself is tacky. I'm sorry you don't get that, but it is.
And why is it
At No Cost to Yourself? Because you didn't personally sacrifice a single thing. You took money you were going to spend on other people and gave it to charity instead. Yay you.

You want to really be charitable? Take money you were going to spend on YOURSELF and give it to charity instead. Taking one person's gift and giving it to another is not charity.
I don't feel guests are entitled to a favor. But obviously you and other posters do. Because if people aren't entitled to a favor, there is absolutely no need to explain to them why they aren't getting one. It would be like having a note at each table saying "You don't have your own personal violinist because we decided to spend that money on charity instead." If you truly think your guests need an explanation, that means you KNOW you have taken money you should have spent on them and spent it on something else of your choosing instead.