People do move on easily. After all, they are driven by their feelings and might cry when others die, but they don't grieve forever. The people close to you will go on because they want to live and have enough luck to make their lives dreamy.
If you think of people as vehicles that move forward, some require more fuel than others. A car requires more fuel when it is heavier and everyone here has it heavy. The fuel you are given during childhood burns out throughout your lifetime. The challenges you face are like mountains and logs, obstacles that require more of your fuel to push through. At the end, when you run out of fuel, there's nothing you can do.
You might be replaced and people might forget about you. Humans are programmed to keep marching forward as long as they have fuel.