"On July 1, 2016, President Barack Obama signed an executive order requiring annual accounting of civilian and enemy casualties in U.S. drone strikes outside war zones ("Areas Outside of Active Hostilities"), and setting a deadline of May 1 each year for the release of such report. However, soon after taking office, President Donald Trump designated large areas in Yemen and Somalia to be "areas of active hostilities," thus exempting them from disclosure. The Trump administration also ignored the 2017 and 2018 deadlines for an annual accounting, and on March 6, 2019, Trump issued an order revoking the requirement. "

The executive order:

https://www.govinfo.gov/content/pkg/CFR-2017-title3-vol1/pdf/CFR-2017-title3-vol1-eo13732.pdf

Trump recinding the order:

https://www.nytimes.com/2019/03/06/us/politics/trump-civilian-casualties-rule-revoked.html

Plus some other dumb shit by Trump:

"During the Obama administration, proposed U.S. drone strikes in locations outside active war zones (i.e., in Pakistan, Yemen, Somalia) required high-level approval. The Obama administration process for approving drone strikes in such locations featured centralized, high-level oversight, based on intelligence about individuals suspected of terrorism activity. Obama's approval was required for every strike in Yemen and Somalia, as well as "the more complex and risky strikes in Pakistan" (about one-third of the total as of 2012), and insisted on deciding whether to approve a strike unless the CIA had a "near certainty" that no civilian deaths would result.

...

October 2017, Trump abolished the Obama-era approval system in favor of a looser, decentralized approach, which gave the military and CIA officials the discretion to decide to launch drone strikes against targets without White House approval. "

All sorts of references corroborating those summary:

https://foreignpolicy.com/2020/05/22/obama-drones-trump-killings-count/

The short version is: Obama demanded accountability and his approval. Which did not exist before and was revoked after. Hence, the different counts of casualties is not representative of an actually difference. Only representative of the GOP being shit.