While I haven't personally worked at such a company, I've observed some "toxic" workplaces and found that typically it is, in fact, the senior staff who are the biggest part of the problem.

Only certain types of people achieve seniority in a toxic organization, and they are typically those who (deliberately or incidentally) benefit from the culture that everyone else hates. They build a clique and try to build influence while the new hires -- who actually care about doing things well -- turn over every 3 months.

This is all anecdotal, of course, but I do think that in an engineering-hostile organization, the senior staff should typically take the brunt of the blame (just as in a successful organization they would take the lion's share of the credit).