Ligaments hold bones to bones, and tendons hold bones to muscles, so they have to be very strong tissue. Muscles are meant to contract repeatedly, and expected to have fast injury recovery. Both actions require a lot of oxygen and steady blood supply.
In order to have a good blood supply, there have to be a lot of blood vessels within the tissue.
Unfortunately, tendons and ligaments do not have any blood vessels that travel through them, or a direct blood supply. While the lack of vessels is what makes ligaments very strong and resistant to stretch, it is also why they do not heal quickly.
The materials needed for tendons to heal are transferred from fluid in blood that is transferred through the tissue. Therefore, ligaments and tendons need to be constantly “bathed” with this fluid since they do not have a direct blood supply within them. This process explains why tendons take longer to heal than muscle. Since movement of the soft tissue helps with the “bathing” process, activity and motion can help aid in and speed up healing.