Usually it's only payable because of a "failure" of long term planning. I.e. someone dies too young before they've undertaken IHT planning, or they've got it wrong in some way (or their professional advisors have got it wrong).
I regularly look at the wills of people who've died, for example, and I'd say more than half the ones I've seen (Relatively "normal" people with estates of less than a couple of million - certainly no landed gentry etc - just people with a decent house and maybe a holiday home or a few but to lets, decent pension funds, a few investments, etc) have taken steps to avoid IHT by use of trusts, lifetime gifts, etc. thus paying nil inheritance tax.
I see VERY few cases where IHT is payable. Usually it's the ones who've died "early" and intestate without actually doing any IHT planning as they didn't expect to die, hence not even making a will!
Advising on IHT is pretty much "bread and butter" work for solicitors when advising on wills etc - even if they don't actually get instructed specifically, it's often in the "default" will template to include simple will trusts.