Why did he do that?

Because Obama created the pandemic response team. Anything obama started, he destroys. 

He’s also cut the budget for the CDC every damn year for the past 3 years

Do not let this be forgot that he not only fired the pandemic team in 2018, but he also most recently refused WHO's COVID-19 testing for Americans in fear that too many positive testing would diminish his chances at a reelection. (X)(X)

And he (or people acting under his direction) are almost definitely manipulating the official statistics, since the data is no longer being sent to the CDC, but instead to the “Department of Health and Human Services”. 

We can’t even trust the numbers to tell us how bad it really is anymore.