On Senior Developer interview questions

Lovely people, and enjoyable interviews but the whole process was very off. Got contacted by the recruiter and started with a 30-min intro call. Although I no longer use the tech On is using, the recruiter suggested me to continue. Then 45 minutes with the hiring manager. He ran out of questions after 20 minutes but I guess we both felt comfortable and happy with each other. Once again, he mentioned they don't care about the language as much and wanted me to proceed. Then it was a 90-minute live coding with two engineers. I chose to use the language I currently focus on instead of my previous main language (which On is using now). The interview went rather smoothly and the interviewers were super helpful and friendly, I felt like they could be great teammates to work with. However, I did say that I'm only willing to switch back to the previous tech stack if the offer is irresistible. After a week of waiting, another HR contacted me on a Thursday to book a quick call the Tuesday after. With another 5 days of waiting, she called me for 3 minutes telling me they wanted someone willing to code in their current language and rejected me. I simply do not understand why they insisted on carrying on with the process even if I asked many times about the tech stack and, more importantly, for booking an appointment of a 3-minute-worth rejection call with a 5-day gap (as if they were waiting for someone first?).