Why not the original coin-op shadow dancer?

I was just wondering, why did Sega choose to release a modified, inferior version of Shadow Dancer on the Megadrive when they could have released a more accurqate port? This baffles me, especially because the Master System version is much more faithful to its arcade parent.

Also wonder why was Magical Flying Hat Turbo Adventure changed to Decapattack? I know it was because of the so called differences in Western preferences but even back at the time it was obvious that they had butchered the original games bright colour schemes and sense of humour, turning it into a bland generic platformer.