I am the opposite of you, a lapsed atheist I suppose. And I noticed that among the religious there is an openness to professing gratitude about everything. Amongst my secular friends, there is rarely a time anyone professes thankfulness (outside receiving something new).
It's not as if the latter are ingrates, but the social ritual of showing gratitude is not there among them, and maybe in some small way, that does breed less thankfulness in the long run...
What is for you the purpose (or result) of (undirected) thankfulness?
I find religious people passionate about following the rituals of their religion (for many more than the intention), in a similar way as atheists are passionate about other rituals (their sport, their eating routines, etc.).
For me the absence of thankfulness equals more with awareness. Should I be thankful I have a house? I prefer to be annoyed other people don't have, or that I can't do better (ex: have a house that generates less carbon, etc.).
The purpose? To remember that what we have was given to us. To be grateful we were given the gift of life. To be grateful that it was given with intention and not randomly.
The result? I definitely find it's helpful navigating the ups and downs in life. Like any other skill, if you practice gratitude you can be grateful even when you've had a significant loss, and it really helps you pull through that. Vice versa you can remain humble through significant improvements in life.
There's a major problem with having too little of a sense of agency. From that we see cycles of poverty and violence from people who seem unable to help themselves. I think this problem is widely recognized.
There's however also a problem with too much agency. It breeds anxiety, discontent, unhappiness. Not everything in your life is under your control, and expressing undirected gratitude is one way of acknowledging that.
I think acknowledging the huge role played by chance in your home ownership (and elsewhere in your life) is very important to stay humble, and to have more correct beliefs and fewer incorrect ones. I call it gratitude.
Not a native English speaker, but when I hear "thankfulness" I kind of hear "to someone/something" (not that much for "gratitude"). Now "humble" I resonate much more with, but I don't see it connected to "thankfulness". People can be "thankful" to someone and feel very entitled at the same time.
Humans have been fighting against "chance" for the whole evolution (chance of starving if you don't catch something, chance of suffering if you take a bug, etc.). I fully agree, you should not feel responsible for it, but you should not like it (or thank it) either.
It's not as if the latter are ingrates, but the social ritual of showing gratitude is not there among them, and maybe in some small way, that does breed less thankfulness in the long run...