Question

Why does the pink color, which forms at the point where NaOH comes into contact with the solution (HCl) in the flask, disappear more slowly near the endpoint?

Answer 1

Answer is: because pH value of solution is changing.
Balanced chemical reaction: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l).
pH of sodium hydroxide solution is above seven (basic), when solution of hydrochloric acid is added, pH slowly dropping until it became neutral solution (pH is equal seven) and that is endpoint of titration.