Metagross has always been popular since Gen III and is used a lot in both Singles and Doubles. Plus it has a Mega evolution and as you all recall, popularity was a part of the reason why some Pokemon got one.
It's Mega is also one of the most used Megas in the metagame as well. Its design is also loved by many.
You make Espeon, Umbreon, Lunatone, Solrock, and Volcarona sad.