# Mathematica gives uncessary condition for integration of $(b - s)^\alpha(s - a)^\beta$

When I compute the integral of $$(b - s)^\alpha(s - a)^\beta$$ on $$[a,b]$$ by the following command:

Integrate[(s - a)^𝛽 (b - s)^𝛼, {s, a, b}, Assumptions -> 𝛼 > 0 && a < b && 𝛽 > 0]


I got an expression with condition a > 0. But I think this condition is unnecessary. Why Mathematica present this condition here?

ConditionalExpression[
Gamma[𝛼 + 1] Gamma[𝛽 + 1] (b - a)^(𝛼 + 𝛽 + 2) / Gamma[𝛼 + 𝛽 + 2]
,
a > 0
]