Got a call from recruiter after a week of posting my resume and had a technical interview for about 5 mins.I was later asked to take the hacker rank assessment.Which I obviously did

The initial call with the recruiter was good and I was excited about the opportunity. Following this I sat 4 hours of technical interviews over two days which were very intense but there were some great people I met on those calls so on the whole I enjoyed it. Where the process fell apart completely was with the offer! I had put my current salary and expectation on the application and mentioned to the recruiter and to the interviewers (current salary and expected were the same). But when I got the offer it was 10k less than my current salary, and this was apparently as far as Amazon could go, which begs the question, why did we bother with the interview process or why wasn’t in mentioned in advance. Bitterly disappointed.