It's a good thing they aren't excessive
What do you think is excessive?
How is it that the government is entitled to anything from anyone's estate at all? No one is being asked to bear the decedent's or the heir's burden. On the contrary, heirs and assigns often bear the burden of having to pay debts, taxes, and any other obligation the decedent has left behind, often having to do so out of pocket. The government does not and should not be expected to compensate them for that. And that being the case, the government should have no right to collect a single dime from any estate, regardless of size.
And how much of a difference will it make, except to manifest some kind of idealistic punishment on heirs? And that's usually the underlying motivation of those who are so in favor of collecting a totally unrelated dead person's wealth from that person's family--to punish them because their family member has entrusted and rewarded them with the wealth they've earned over their life.