Could be for a variety of reason, like the head skin producing oil itself. Do note that applying too much oil on head, and for too long, can actually cause blockage of air to the roots of the hairs, causing them to fall easily. Check the patterns. If something produces even minor positive effect on hair fall, stick to it and leave others. Don't massage your head or apply towel to hair vigorously after a shower. When something is weak, you must not apply force to it, as it will only result in more hair fall.
Don't go for hair transplant, it's expensive, non permanent 90% of the time, a waste and may destroy your brain as it destroyed the brains of the sharif brothers.
If everything fails, make the following guys your ideals quickly. Some men look more handsome when bald than with hair.