It's not the usual thing about knowing they won't suffer any consequences for their behaviour?
I think that's an element.
Every time I've heard someone talk about absolutely awful managers, they're always small firms directly run by the owner. Because, of course, there is no system to hold these sorts of small business owners to account. I strongly suspect MPs are similar, because they are likewise their own bosses to a large extent. There are systems within parties, and systems within government, but these tend to be weak.
You average major corporation has all manner of processes and guidance for staff to deal with each other (that's one of the major jobs of HR). As someone rises up through the system, they will either receive formal training or be expected to pick up from experience and example proper ways of behaviour. MPs obviously don't. One might expect many MPs have experience outside politics where they may have learnt this, but skills can also degrade with lack of practice. In Westminster, what ends up happening is that a very senior civil servant will take a minister aside and tell them that their behaviour is adversely impacting their department. But that's not a formal process, and there's no clear system of, well, professional development training. It is just hoped that the minister will try to do better.
The standards that applied to ministers originated in the 1980s as a confidential guide, but was formalised and made public around 2010 as the "Ministerial Code". Most of this relates to potential conflicts of interest and so on, but it also includes elements of how to treat civil servants appropriately. Raab is just the latest in a series of issues regarding ministers breaking the code.
What's evident is that there's significant pushback from politicians about how they are expected to behave. My sympathies with a lot of this run relatively thin - they do strike me as people who expect to masters of their domain with minions to order around, rather than leaders with responsibilities towards the people working for them.