He is making his future defense lawyer's job very difficult by committing to a story. The lawyer will be severely constrained from suggesting alternate explanations of the facts to the jury because SBF has already negated so many possible interpretations. Every time SBF overstates an explanation, the prosecutors get that into the record. Every time SBF provably misstates or misleads in an interview, the prosecutors get to say "take a look at this slime ball."
When under investigation, you shut up. It's the only smart thing to do.