Technically we call this day a festival, a festival not for the living people, but for the passing away people. Although we Chinese people officially are all atheist, most of us in general believe in Buddhism.
The origin of Buddhism is surely from India, but the Buddhism in China nowadays is a independent religion system based on Chinese culture, so basically you can call it Chinese Buddhism.
Like most of the religion in the world, Buddhism also think there will be the afterlife, people who passed away would live in another world, I don’t not have the exact theoretic philosophy knowledge about the Buddhism, but it still got heaven, hell kind of thing out there, karma as well.
In ancient time of China, even nowadays, Chinese culture tend to be paying more attention to the death than the living , one example is for most people, they would rather want a decent funeral than a decent life in their last days if they have to make a choice.
People need ritual to approach the meaning of life, I have talked about the common procedure for the funeral here , and when all of this is over, the tomb sweeping day every year is the regular day for people to remember and mourn the deceased people.
For most Chinese people, the bone ash of the deceased people would be put into a grave yard in suburb area, just like a real estate market, you have to pay for the burial ground place in the grave yard, depending on the SQM you need, it would cost you from 1000RMB to 100,000RMB($15k), there are even expensive one, which can be used as an investment. Although the government try to regulate the investment on the grave yard market, but it is still a profitable business for lots of people.
Every year around the tomb sweeping day, the road to the gravy yard would be severely jammed, you basically can not have the serenity time when mourning for your family or your friends, but people seems to be getting used to it already.
Sometimes, I have to think, why people can not choose the deceased date as the anniversary day, just have your own time to mourn for the deceased people. If would die in some day, I don’t want the people I ever loved to remember me like that, bounded by the so called ’culture’, if they really love you, they would remember you all the time, not the single tomb sweeping day. And also, If you did good enough to your families when they are still in this world, you don’t have to do much for them in another world.
Do something when the one who you love is still alive is way better than do anything in the grave yard which can only be seen by others, not the one you loved.