it is no surprise that debt and owing are strong themes throughout the hunger games series. katniss "hates owing people" (thg, 32). because, for katniss and the rest of the people in the seam, relationships are transactional.
when katniss first meets gale, their entire relationship becomes transactional as katniss offers him "a bow if he had something to trade" (thg, 111). knowledge and goods do not come freely in the seam, and everything must be met with a trade, even relationships.
so, owing suggests a debt that will have to be repaid, something that can constantly loom over a person who is already pressed to use all of their resources for their immediate needs. this uncomfort with debt is not limited to district 12, but spans across the entire country. this is made clear when thresh spares katniss because of the love and protection she gave rue, making it so that they were "even then. no more owed" (thg, 288).
it is even ingrained into the rhetoric about the games. the games are put in place because of what the districts "owe the capitol" because of the rebellion (thg, 42). the games are meant (at least in concept) to be an indemnity, a repayment.
so it is not a coincidence that our favorite boy with the bread doesn't live that way. katniss doesn't expect peeta to understand the disdain the people have for debt because he has "always had enough" (thg, 292). and, despite peeta getting annoyed that she thinks he's "too dim to get it," he doesn't get it (thg, 292).
for peeta, he doesn't get why thresh would spare katniss just to get even. and he especially doesn't understand why katniss owes him for the bread. because he gave katniss the bread without any expectation that katniss needs to do anything for him. because he did it because he cared about her, not because of what she could do for him in return.
and i think that it is interesting that, in the second book, peeta tries to persuade haymitch to save katniss using the rhetoric of debt.
and i can totally imagine how it must go on in his head. that he remembers how katniss mentioned that people from the seam hate feeling indebted to others. so, he is going to use this against haymitch to get what he wants (cf, 49). and the funny thing is that peeta still shows that he doesn't get it. he still doesn't understand how these transactions are supposed to work. because he doesn't use haymitch's debt to benefit himself. rather, he invokes haymitch's debt to him to perform another selfless action (cf, 50). to save the girl he loves. and leave it to peeta to take a transactional relationship and still center it around his unconditional love.
and that is what makes peeta's second invocation of debt so heartbreaking. in mockingjay, when hijacked! peeta considers finnick saving his life, he says that it didn't count because it was "for her" and that he didn't owe him anything (mj, 208). this is just another way that hijacked! peeta seems to have changed who peeta was. peeta no longer considers acts that protect and care for katniss as good enough to justify his indebtedness (and that is pretty constant throughout katniss and peeta's feelings about each other).
so yeah, he finally gets it. he gets how debt is supposed to repayed and how relationships are supposed to be transactional, and it destroys katniss (mj, 208).
but that is what makes peeta's return with the primroses even more precious. because he "went to the woods [that] morning and dug these up. for her" (mj, 325). he did it for prim. for a dead girl who couldn't possibly repay him. because she needs to be remembered in a world that refused to acknowledge her. a world that thought she was disposable. and it signals that katniss's peeta has returned. and now, he understands how debt is supposed to work, but he doesn't invoke it. he does not subscribe to a system centered on transactional relationships.
because, although snow tried so hard to convince him of it, that is not who peeta is. he loves unconditionally. he memorializes children that were deemed disposable. he refuses to forget. and that is why katniss loved him from the start.