Parallel Domain interview questions

Pretty standard process, with initial HR screening then a follow-up up more focused interview for round 2. They asked basic experience questions, what I thought product management meant etc. They were building the function from scratch and sounded like they needed a more senior PM hire for the first position.

The interview was very lengthy but their response time was quick. They mailed me for an opportunity in their company. Initially they started with a non-tech role but as per my domain they shifted me to tech roles. There were multiple rounds. I had to go through 2-3 initial rounds, then 1 hour phone screen round where I had to code in Python and run that code too. Questions were mostly on hashmap and I was able to run all the programs. Then they decided a round with hiring manager and he gave me an overview of the onsite. for onsite, I have to prepare a presentation on my greatest achievement. I thought it went well as everybody was appreciating it. then the same panel interviewers took separate rounds about 4 rounds more in which they asked technical as well as maths questions. They asked me to show my GitHub (if I am comfortable). The process went smoothly but then the next day I received a rejection email asking for further they said I have lesser work experience and have made their decision. I felt the interview went really well and my work experience was very transparent in the initial 2-3 rounds. I felt this wasted a lot of my time and energy.