According to a Premium Times report, the main reason President Muhammadu Buhari doesn't want the SSS to be in charge of security at Aso Rock is because the institution is compromised and still has loyalists of past governments who could set booby traps for him.
A top SSS official, who said he repeatedly warned his colleague against partisanship, said days before he stepped down, Mr. Jonathan “rewarded those who helped his cause”.
“President Jonathan caused the promotion of those who were loyal to him, some did not even sit for promotion examinations. Many of them were not yet due for promotion. But they were arbitrarily rewarded. Some people were hurriedly deployed to sensitive positions and this might be a bobby trap for the president,” he said.
At least 45 officers of the SSS, including its spokesperson, Marilyn Ogar, were promoted to different grade levels during a controversial hurried promotion exercise in the dying days of the last administration.
It is believed that President Buhari was fully in the know of all that transpired at the time and had waited patiently to act.
“The President feels that SSS personnel should not be close to him until proper reorganization of the agency is carried out,” he said.
However the presidency says it's a routine adjustment.
The Real Reason Why President Buhari Doesn’t Want DSS Operatives Around Him - PT
Nigerianbulletin