Also, it is a good opening for discussing specifics, why use one or the other, what problems have you experienced using that container etc.
And to answer OP; There can be myriads of reasons why you are not getting a job, but just reading this short introduction to who you are, I already know I'm not hiring you. You seem to think having a Ph.D entitles you - I'd rather hire someone with a solid foundation in theoretical CS, but with years of practical experience; that is someone who got a b.sc or perhaps a masters, but worked her ass off getting pratical experience. People with a Ph.D is quite often not a good fit in a work environment, you tend to have a very very good knowledge of a very specific field and in CS that is basically a death sentence - we want people who gets excited about all the new shiny, yet still have the fundamental understanding CS.