Because of the facts:
While the FBI had suspicions in 2010, before the uranium deal was consummated, they weren’t confident until four more years of investigations had been concluded, and that was well after the deal was done.
Whatever the FBI did know in 2010, there is no evidence that information had been communicated to Clinton or to Barack Obama. There were even numerous high-ranking FBI officials who didn’t know.
Not only was the decision not Clinton’s to make, it’s likely that she played no role, having delegated the seat on the nine-person Cabinet-member council that evaluates these situations to an undersecretary
The great majority of the $145 million donation to the Clinton Foundation came from one person, and while that person was once affiliated with the Russian company that bought the uranium, his association ended half a decade before this particular transaction.
Even if the $145 million HAD come directly from the shady Russian uranium buyers, that is certainly suspicious, but WOULD NOT be prima facie proof of a quid pro quo arrangement.