Spoiler: No scientific reason.
Fibonacci grows exponentiallyvery fast, so people will have fewfewer options before reaching enormous values; thus it incentivizes breaking work down in smaller pieces.
If the smallest typical work takes 1 hour, a big piece may take 8, 9, 10, ..., 16, ... even 32 hours.
However, if the smallest piece of work takes 1 story point, and they grow in Fibonacci, a big piece may take only either 8, or 13, or 21, and only if you stretch much 34 story point - 4 options to pick rather than 24.