Why is sun exposure bad after hair transplant. Very confused. Would like a clear answer. PLEASE!

Sun exposure is not recommended after surgery but if it already happened there isn't much you can do.  Ultraviolet light from the sun can permanently discolor your skin if the wound has not healed.

A brief sun exposure at nearly 2 weeks post op is unlikely to damage grafts. By the 2 week mark, you should be returning to your baseline hair care regimen. Damage/loss of the grafts at this point will typically require an equally traumatic insult as the process that placed the grafts initially.
It is important to remember that exposed scalp will be sensitive to sun exposure and can more easily tan/burn/bleach. These changes can be permanent and thus it is advisable (irrespective of procedure) to take reasonable sun protection precautions.
As always, discuss your concerns with a board certified plastic surgeon (ABPS) with experience in hair restoration.

We typically recommend our patients stay away from any sun exposure for 90 days post transplant. Reason being is because it could potentially damage the grafted area as well as causing skin sensitivity on the grafted area of the scalp. If you are going to be out in the sun we recommend that you wear a hat. 

Sun exposure can dry out the transplanted area, cause sunburn and skin damage, and impair healing.  However, a single ten-minute exposure two weeks after your procedure is unlikely to cause any problems. 

Hello, Thank you for your question. The sun exposure is not advised for the first 2 weeks after the surgery. The reasons for that are: The sun makes healing process weak and slow, also since you are fresh from the surgery, the sun might burn your skin, which will cause you some additional cosmetic issues such as sun burn marks or red dots. Since you were 14 days post op and spend only 10 mins under the sun, it should not be a problem. But my advice wear a hat whenever you go out doors, at least for 4 weeks post-op. 

Sun supplies ultra-viiolet light which impares healing of any body wound. For this reason, all wound should be protected from UV light