Query : Strange hiring behaviour ?

I recently interviewed with two companies (big name tech and retail+tech). These were for junior programmer/software engg (1-3 years). I was through the technical phone screeners and both companies asked me to schedule on-site interviews. This was a few weeks ago. Since then I haven't heard back from them even though I've sent them weekly reminders. I find this behavior very strange, rude and unprofessional. Note these are well known and well established companies in the tech and retail+tech sector.

Why would they behave like this ? Is this because of a job slowdown/hiring freeze ? Shouldn't they at least let me know whats going on ?

I'd like to know if other people have had similar experiences.