"The developers" do not exist. You mean the core project which has it's own developers. Their work may be adopted, but that is a consensus issue and is not their decision. Anyone with an idea to improve bitcoin is welcome to write code and let the bitcoin community make their choice about it's merit. So for me there is no conflict of interest because they do not represent bitcoin, they only represent themselves.
Nobody can deny that lots of core developer work for blockstream. Yes the consensus may stop some one do something evil, but it's also stop people do something good, this is the real problem.