What were the differences between Mark Fogel's and Brittney Griner's releases from Russian imprisonment?

Mark Fogel, an American teacher imprisoned in Russia for three and a half years on drug charges, was released without any prisoner exchange, unlike WNBA player Brittney Griner, for whom the Biden administration had to trade a Russian arms dealer to secure her freedom. Fogel's release came through apparent diplomatic channels, with former President Trump thanking Vladimir Putin for freeing him. After his release, Trump welcomed Fogel to the White House. This contrasts sharply with Griner's case and demonstrates different approaches to securing the freedom of Americans wrongfully detained abroad by Russia.