It's true! Just like other interviewees mentioned, it seems they are interviewing just for fun's sake or to train their engineers.

I went onsite for a two-hour interview, one coding and another design.

The coding question was purposely very hard. I was still able to find a solution step by step. I also gave a correct solution for the design problem.

But during the whole interview, I felt that it was not a purposeful interview, nor was it conducted with the intention of hiring someone or getting to know the interviewee.