Goldman Sachs Software Developer interview questions

I was referred by a friend. I interviewed at London, UK. The process took nearly 4 weeks. Round 1: Coder Pad interview: 2 questions that I solved in 40 minutes. They are not so hard, greedy algorithms + mathematical puzzles style Round 2: On-site round 1: problem solving with data structure: Binary Search Tree, HashMap Round 3: On-site round 2: problem solving that you can formulate as find number of connected components in a graph (so use DFS), sorting Round 4: On-site round 3: problem solving related to database: Hadoop style question Round 5: On-site round 4: System design: design a system that supports review and send documents, how to scale Round 6: On-site round 5: Behavioural questions (how to deal with deadline, motivation, etc.)

Rejected in 1st round. It was a Coderpad interview, there were two questions and I answered both of them. I don't understand why I got rejected. I don't understand why they even interview people when they don't have the intention to hire. Very dissappointed and hit on my confidence.