Why?  Because that is who YOU are.  (a gentle reminder.  

)
I don't change based on how other people behave.  That would make me a reactive person, just reacting all day long to "stimuli".  I'm my own person. 
I am courteous because I believe it is the best way and also because I try to cultivate virtues in myself (don't always succeed) that I think are beneficial.  
TNT is generous.  That is who he is.   And yes, it was disappointing to not receive a thank you. maybe she was shocked, who knows.
But I think it is wrong to give any kind of gift with an expectation.  A gift is freely given.  
It wouldn't upset me THAT MUCH if somebody doesn't say thank you.  That is on them, not me.  I have my own path, they have theirs, I have enough of my own lessons to learn and practice and really don't have energy or time to worry about "what other people are doing or not doing."   Once I got to that point things started to flow a lot better in my life.  
Well, I'm not always on point, but I TRY to be that way.  Annoyances are still there of course, I"m human, but I try not to get caught up in it.   I am older though, in my 20s this stuff used to drive me batty.  
I just know that i have way too much improving to do on myself to devote much thought to how others can improve themselves.  Unless it's somebody in my immediate family who I have to deal with on a daily basis.  Like mom.  who I recently had to tell her she was bordering on stubborn in her old age, adn that is not a good trait.  Her tenacity, in youth, while trying to support and raise 4 kids was good and an asset.......when no longer needed to do those things, it can turn in on itself, and just turn into stubborness, which is NOT good.