Being grateful is an incredibly subjective state of being, and its impossible to say that people can or cannot be more or less grateful due to varied reasons. People can be incredibly grateful for one thing above all others, and people have varied reasons as to why they are grateful for reasons.
It is very easy to feel more grateful for one thing than for another. For example, I am very grateful for an unexpected gift than I may be for a gift card to a place that I never go to. The intention behind a gift can also help how grateful i feel about it.
Of course the whole point is to cultivate an attitude of gratitude that permeates all of life and everything we have and are. But initially one is just going to pick particular things that one really values such as certain relationships and that is going to help one become more grateful for everything.
People are able to be more grateful for one thing over others. That is normal, one thing may have saved their life, while others are just nice gifts to have or nice items. I would be more grateful for the gift of life than other objects in my life because I get to still enjoy them with each breath.
I believe it is very easy to be more grateful for some things, rather than other things. I think being grateful is very subjective to what the person needs. For instance, if I ruin my last pair of jeans and can no longer wear them, I will appreciate and be more grateful for a new pair of jeans, since I have none. If I had ten pair and received an eleventh, I would obviously be less grateful for the new pair.
The notion of being grateful is a social construct based on two factors, namely expectation and reward. We assume that if we do something for someone (expectation) then we will receive some kind of reward, whether it is a "thank you" or a favour in return or whatever. People may express gratitude, but there's no way to know if the expression of said gratitude is "authentic" or not. In addition I think gratitude, or the illusion thereof, is based on novelty and therefore another construct: time. For example, I buy someone a gift, and they say thank you and tell me how grateful they are. Now after some time they get used to the gift, and so it becomes something commonplace or expected. Are they still grateful then? What happens if the gift breaks or somehow causes them to have an accident? Are they still grateful then? It's totally fleeting. In addition someone can say they are grateful to have a job but complain about it the very next day. It's completely subjective and contextual in nature, and as soon as something bad happens, gratitude goes out the window, even if only for a little while. Gratitude is at best a social convention, but realistically it's totally non-existent. It also fascinates me when people say how "blessed" they are or how they are so grateful to be alive...Right now maybe, but not for long. I'm not even sure people really know what it is to be grateful or how to really express gratitude. We shouldn't have expectations, but it's unavoidable. We shouldn't expect rewards, but that is also unavoidable. I'm not sure humans can do anything with "the right heart" or love someone "the right way." As long as inherently selfish humans are involved, there can be no resolution to things. It's just one big circle, a routinized, cyclical existence that plays out as it does, and if we cannot escape ourselves and thereby be completely unselfish, how can we ever be "grateful?" It's a damn paradox. All of it is.