Because guidance is management's own number, raising it carries more weight than beating someone else's estimate. It resets consensus-estimate directly and usually triggers upward estimate-revision across the coverage list.
Read the composition. A raise that only passes through a quarter already banked is weaker than one that lifts the second-half assumption, and companies word the distinction carefully.
Example: Northwind Tools lifts full-year EPS guidance from a $0.94 to $0.98 range up to $1.00 to $1.04. Roughly half comes from the quarter just reported and half from a better second-half margin assumption.
Related: guidance, guidance-cut, consensus-estimate, estimate-revision, earnings-beat