BrowserStack Senior Software Development Customer Engineer interview questions

1st round was telephonic interview on technical aspects. Once selected, received a call from HR after a week for 3 more rounds which were to be conducted on same day. 2nd round: given practical assignment to be completed in 2 hours. This round took 3 hours (10-15 mins were given to everyone to explain what has been done in given practical task). Cleared this round. 3rd round: given task to create power point presentation on one of the products in 1 hour. After 1 hour had to give explanation on it for 15 mins. 4th round: Managerial round (technical + managerial questions were asked) All rounds went well. Received an email from an HR 'We are sure you enjoyed interacting with the technical team solving the problems that were presented to you and we appreciate your efforts. However, we think that something was amiss. Hence we will not be able to move forward at this point of time. We would love to connect with you in future' What hurt more is : I did give my best for last 3 rounds which were conducted on same day, was exhausted, tired and result is 0. And explanation given by HR was pathetic. If you don't want to select candidates then why do you waste time of others.