The answer is pretty simple: Samuel himself asked for a trade early in the offseason. According to ESPN's Adam Schefter, Samuel asked San Francisco to move him during his exit meeting for the 2024 season. The team then granted the wide receiver and his agent, Tory Dandy, permission to find a trade partner, which wound up being the Commanders.
After sending Deebo Samuel out east via trade, the San Francisco 49ers turn their attention to other pressing needs.