Unfortunately this happens and should not be happening.
I used to pick up the tray myself the times I went to a fast food restaurant after eating. But, after I was told something by a friend I am not sure if picking up the tray after eating is something good. He told me, employees are paid to pick up a tray, there are just 2 tables occupied, and if you see these other tables where clients picked up the tray by their own, you can see that the tables are dirty, and there are enough employees to clean the tables here but they don't. I thought he was rough at first, and I disagreed, but then I started to wonder if picking up the tray in these cases was correct or not after observing other attitudes: Many times I see employees that do not care about the client, they do not care if there are napkins, sugar, ketchup, if the tables are clean even when the clients pick up the tray, and you can see employees sometimes watching TV, a football game, etc. and even to shout if there is a goal when the place might not be even OK. Also, if the clients pick up the tray, this will let big companies to save $ with less employees, reduce salaries, etc. So basically I was told to pick up the tray by some persons, and I was told NOT to pick up the tray by others, in both cases I was said this in a manner I did not try to discuss.
Regarding to offer the sit to an older person, I offer my sit, but it happened to me something very strange once. I offered the sit to an old woman in a bus who can hardly walk in my opinion, and the old woman (75-80) said, I do not need the sit I can walk by my own, I will just travel up to the 2nd bus stop ..., I insisted but then she answered me in a way I did not insist again (she was not insane, but I think she was crazy). Then, in the next bus stop, other woman around 40, started to shout at me saying that I did not offer the sit to the old woman, so then I got judged first for offering the sit, and then because the other woman thought I did not offer the sit. When the 40 year old woman understood that the older woman did not want to be treated as an elder woman she did not say anything. This old woman made me remember to the Condesa de Chikof, an old woman who said that she was going to live more than 100 years and never said how old she was, she did not take warm water bathes, she just took cold showers in order to have a healthier life, etc. etc. but what I heard from her in her last years is that she was old and did not take cold showers anymore because she got sick, but well... it it is something strange in ARG to me, but it seems it exists, and is better not to discuss sometimes.