Generally, we like meat to e tender and juicy rather than tough and dry.
And when the cooking goes on for hgours, the fiber bundles fray away from each other, and even tough meat begins to fall apart...
Simple physical damage to the muscle fibers causes them to release more of their fluids and therefore more stimulating substances for the tongue.
Cooking intensifies the taste of meat and creates its aroma.
The texture of raw meat is a kindk of slick, resistant mushiness.
The fluid release is at its maximum when the meat is only lightly cooked, or done 'rare.' As the temperature increases and the meat dries out, physical change gives way to chemical change, and to the development of armo as cell molecules break apart and recombine with each other to form new molecules that not only smell meaty, but also fruity and floral, nutty and grassy (esters, ketones, aldehydes)...
This early reference notes this stage is unwholesome [Markam]. Medium/medium rare were introduced about this time. Originally only of eggs: slightly or imperfectly cooked, underdone. And indeed, among winged creatures they can eat with pleasure wood pigeons still running with blood and scarcely touched by fire.' Bruyerin advocated the middle way, warning that there would be a penalty to pay for eating either half-raw or 'melting' meat.