One answer to why we care about the welfare of society, is because it helps us directly. This is not just about charity, but truly about why we care about our community so much. If you think about it, many people are literal strangers. But still people go out and work in the public service, devise solutions for mass use, and innovate solutions to hard problems.
It is not just about the material rewards either. Because clearly a sense of mission and purpose exists among people.
The Western view that we are all individuals may be incomplete. It is not hard to reason from the point of view of a collective. When a close one passes away, you feel hurt. They may be a distinct person from you, but they are clearly more than just another person.
Likewise with all of us combined. Humanity is a real concept that is present in all of us. This is just like what nationalism has done to create a sense of unity in a country. And it is also present in the new notions of being a global citizen. Perhaps that will come to pass in the future and be felt even more keenly.
For now, compassion is not a weakness, but merely comes from understanding that we have a common humanity. The good things in life: connection, culture, service, are all present in ourselves and in others. Uplift others for these ideals.