There is no reason for anything ever, existence itself has no reason at all... what is your point exactly?
You can certainly convince yourself what you do has a purpose, but it is delusional utterly. Every faith says this creation will some day terminate, so even if you say you are working to improve the world, eventually it will be no more so it is pointless. Whatsoever we accomplish will be destroyed some day, whosoever we meet in this life, both us and them will eventually be dead so what is the purpose of it?
Meditation creates a space where you can know that which is permanent, that which will persist even after this universe ceases. Not only that, but as in the example of Bodhisatva's, the enlightened mans energy can effect all around him - you can set creation in a certain direction merely by willing it enough, this is why Christians are taught to pray... it is the same phenomenon only the normal person has very little energy. You meditate to procure energy, you work to still the mind so that less energy is wasted in it. Eventually you are surrounded by energy, it is utterly overflowing and reaches to everyone around you. Now there is a great responsibility, now if you think anything negative, you simply watch and chaos will ensure. Then, if you think something positive, beauty ensures... THAT is why I meditate.
For me, everything you claim as your good actions is naught but superficial busy work. You think you are accomplishing something, but it is nothing in the larger scheme of things. It is so petty and small it really is a waste of time, utterly.