I mean, which holiday cards do you prefer? In my book, on a scale from 1-10, the 1 cards are those that have a generic, pre-printed message with a signature from the sender. A 5 is usually the one-size-fits-all letter. Bonus points (like up to a 6) if the letter is witty, and maybe 7 if it includes a photo. But the best cards are those that have a personalized message written to me.
We all want to feel valued, loved, and appreciated, and nothing says "I value, love, and appreciate you" like a hand-written note. When we invite others to our wedding, we are often asking them to trek hundreds of miles, spend hundreds of dollars on a plane ticket/rental car/hotel, and perhaps take a day off work. It seems like a little note of pre-appreciation is in order.
I don't mean this as an attack against generic invitation senders. I'm genuinely asking, "Why is it more customary not to write anything personal on invitations?" Is it because guests lists are usually very long and it would take too much time? Is it because invitations are often very beautiful and you don't want to sully the appearance?
Any comments with your speculations would be greatly appreciated!