Becaus he love her lover very much and wanted to marry him and her father was against her decision so she decided to elope with lover.
1 2 1
Lord Ullin's daughter wanted to elope as their father opposed to their love and did not want his daughter to marry her lover (for reasons unknown). To save their love both of them eloped and unfortunately died, making Lord Ullin regret the fuss he made.
1 5 1