The pay differential between these roles is mainly a factor of supply and demand, not necessarily due to the relative difficulty of actually doing the jobs. Most jobs which are "social" rather than "technical" are actually harder in some way, but they have as massively lower barrier of entry from a credentials/skills perspective so tend to be significantly lower paid than "technical" jobs.
Digging ditches is a lot harder than writing code all day in an air-conditioned office, yet ditch diggers who aren't credentialed machine operators get paid significantly less than software developers because the only qualification barrier to be a ditch digger is to not be physically disabled or unalive, if you can fog a mirror and walk from the truck to the hole to be dug and operate a hand shovel, you can dig a ditch.
Supply/demand doesn't care how difficult your job is, it only cares how many people are capable of doing it compared to the number of people needed to perform it. In a very dollars and cents sort of way, the time of a technically skilled person is more valuable than the time of an HR person, which is why it's very rich that they think you're wasting /their/ time, rather than the other way around in these situations. The candidate's time is actually more valuable in demand dollars than the HR person's time, especially recruiters which are one of the lowest barrier roles you can have in HR.
Not it isn't. I haven't dug ditches, but I've done other physical labor. At the end of the day your body is exhausted, but your mind is still sharp and ready for more. By contrast when programming all day your mind is exhausted, but your body is ready for more. Different types of hard, but both are very hard in their own way.
Actually most ditch digging these days is done with a machine. I don't know how hard that is, but I assume it moves more to the repetitive mental work side.
There's hard as in effortful, which certainly you could make the argument that many jobs eclipse software or other technical positions.
And there's hard as in difficult, or technical, or complicated, etc. This is more difficult to describe since what's complex or impossible to one person is trivial for another.
The second bucket is how most technical jobs play out. It's easy to write off the "get skilled" requirement of these jobs, but that's usually a difficult endeavour itself, usually involving a few years of higher education (in the normal case)
I agree with everything up until this portion. I think HR can be a very difficult job, in a way that's quite similar to say security positions. If an HR person excels at their job-- you will never see them, you will never interact with them outside of paperwork, and you will never need to ask them anything. So it can be very easy to assume HR is doing nothing. In reality good HR manages multiple complex, competing organizational systems (office politics, board concerns, retention, legal, recruiting) and is expected to manage them in such a way that none of the competing organizational systems are even aware of the friction, while having none of the power to actually change anything by themselves.