All right, I'll do this.
It's not so much the cost without the return. It's the thinking behind it. The tenant's two most difficult rent payments are December and January. As they write the check out for December, all they're thinking about is how far this money would go to make their children's Christmas better. As they write the check out for January, many of them have made significant sacrifices to have that money in their account post-Christmas. Many of them have taken on extra hours and extra side jobs to cover increased holiday expenses. They are not thinking very kindly of you during the holidays to begin with.
If, in between the hurdles of those two checks, they should get a $25 gift certificate to Pottery Barn or The Spa Store, that's immediate proof that you don't understand what they've gone through, the life sacrifices they've made, to get you those checks. The past few months have seen precious few trips to such places. And February's a short month, too.
If you send a $25 gift certificate to Walmart or Costco, you're just a cheap bastard.
If you pass along a few cookies your wife managed to bake, all they're thinking about is that their sweat, blood, and tears went to fund her free time potting around in the kitchen, having the perfect Christmas while they were sweating through doubles at the plant.
Maybe you think that if you cut them a $50 or $100 break on the rent, that would be nice. In which case they're thinking that you don't really need $50-$100 bucks on the rent every month and that's just gravy for you.
And when you present the gift, they are of course expected to be grateful. Maybe handwrite you a little card telling you how wonderful and thoughtful you are for your gift certificate or baked cookies. They'll feel pressure to reciprocate, further depleting their already strained resources. All so that the landlord can feel he's a good person.
For broke people, Christmas is a time of extraordinary monetary stress and the same depression that afflicts everyone else. The holidays are a time to rethink one's life. What should they rethink? That they're living in a house they don't own with a landlord who's making money off them? That you have these wonderful passive income streams to have yourself a very merry little peaceful Christmas while they grunt and sweat through these weeks just to make ends meet?
You are not their employer. You do not pay them, and so your gift is not a bonus, an additional payment showing your gratitude or recognition. You are not their business partner, making a traditional holiday gesture that indicates your goodwill and willingness to continue your mutual enrichment of each other. You are their landlord, an ancient cultural archetype of greed and cupidity, taking more than you deserve for what you offer, ready at a moment's notice to throw them shivering on the street and strew their belongings across the yard should life's vicissitudes overwhelm them one fine month and they're unable to pay you.