SEGA MEGA DRIVE strip of colored pixels on bottom screen

Something that has always baffled me playing the SEGA Mega Drive since I was a kid back in the day, what was that strip of colored pixels being displayed on the bottom part of the screen on every single game as if it was a defect, until I recently discovered that it was actually the exact color sample used for each scene. But why did the machine have to do this?! Other consoles and computers, arcades of its time like the NES, SNES, PC-Engine, NEOGEO & AMIGA didn't have to do this?! It's also surprising of how few colors the Mega Drive displayed simultaneously on screen which was even less that 24 in many cases from a total of only 61 colors on screen, when 256 colors on screen or more had been established as a standard since the mid 80s on all Arcades, PC (VGA), AMIGA, SNES, PC-Engine showing how poor the Mega Drive's palette and available color gamut was. Even the SEGA MEGA CD didn't improve things as seen in Shin Megami Tensei in these screen-shots.

https://i.postimg.cc/XYsQGC2K/01.jpg

https://i.postimg.cc/g2zg2DKk/02.jpg

https://i.postimg.cc/0QwfBH9Z/06.jpg

https://i.postimg.cc/8Cswhz32/11.jpg

https://i.postimg.cc/FKqpGQX7/15.jpg