Why didn't Watson and Holmes have stapleton arrested after Selden's death?

Watson and Holmes did not have Stapleton arrested after Selden's death because they lacked sufficient evidence to directly link Stapleton to Selden's demise. Although they suspected Stapleton's involvement, the circumstances surrounding Selden's death were ambiguous, and they needed more concrete proof to justify an arrest. Additionally, Holmes was focused on unraveling the broader mystery of the Baskerville curse and ensuring the safety of Sir Henry rather than immediate legal action against Stapleton.