Because centrism represents opposition to any upset to the status quo. Centrism is less about social or fiscal or foreign policy and more about whether the next administration represents a major shift away from policies traditionally implemented. I'd reckon Gilded Age centrists opposed the forty-hour workweek and workplace safety standards until those things became the norm. No research done. Just a hunch there.

Change represents instability, and instability represents a need to change one's behaviors to succeed in the system in place. It's not about right or wrong or left or right. It's all about not changing the rules of the game. It's laziness disguised either as an unwillingness/inability to choose a side OR "bOtH SiDeS!!!1!!1!1!"

A failure to choose is still a choice. One absolves himself of no responsibility by keeping in place the evils that make our society function in its current state knowing there is a way to run it without said evils. It's a knowingness that the transition to better outcomes will be painful in the meantime, so to avoid ripping off the band aid, they bury their heads in the sand and pretend each side is just as bad as the other.