Looks like he stepped down to stop investigations into the Frontier Foundation, a scam NGO for nepotism and transfers of wealth?
I thought you might be exaggerating, but if the wikipedia entry is to believed it seems like a pretty obvious case of laundering bribes:
"In 2003, Buyer created The Frontier Foundation, whose stated purpose is educational funding for college students ... Buyer's daughter Colleen was the president ... His son Ryan, in 2009, was director ... the foundation shared an office with Buyer's campaign office ... annual fundraising golf outings had raised more than $880,000 for the foundation. Almost all the contributions were from 20 companies and trade organizations that had interests before the House Energy and Commerce Committee, of which Buyer is a member ... In 2018, the Frontier Foundation was closed by Buyer, the only listed officer, without ever having funded a scholarship."
Excerpts from: https://en.wikipedia.org/wiki/Steve_Buyer#Frontier_Foundatio...
22 months is embarrassing, that no other agency could put him away first is even more embarrassing.
The word "scam" is a redundant modifier for an NGO :)