Beam Living interview questions

Straightforward interview. Was offered a position then rescinded offer due to supposedly "conflict of interested" even though information about this was given to them since day 1 before interviews were conducted. Rejected an offer to another company with higher salary due to their initial offer. How do you go through 4 plus rounds of interviews, offer letter and all parties sign, and then call to rescind the offer. This does not seem like a very effective way to interview/hire a major waste of multiple individual's times.

There were 3 Rounds, The first interview had 2 managers, 2 an assistant and a Manager, then the next round a Senior Manager and a different assistant manager, then this round the boss above the senior manager.