That's literally what gravediggers do though?

Not that they have much work these days, everyone's going for cremation and then bury a small urn, so the grave doesn't take much time to dig. But till now, yes, graves have been dug by humans. Letting noisy and polluting excavators into a graveyard, which is supposed to be a place of quiet contemplation and respect for the dead, would be preposterous. Why even dig a grave if not out of respect for the dead, and what kind of respect are you showing by having a machine do it all in 5 minutes?

Here's a 14 year old article about the gravedigging profession and how they have less work nowadays

Here's an 8 year old article about an 83 year old gravedigger. If he could still do it, so could anyone (except for people with actual disabilities of course).

Both in Estonian, but you can translate it.

Sure bruv, you go dig a grave by hand.

I've dug one myself, for most we've used a professional gravedigger's service though.

We’ll see how long it takes

Usually it's not really done for efficiency. It's not particularly efficient to have a bunch of people sit around for a wake either, if they could all be at work instead. It's all a ritual essentially.

Anyway, you can have it done in a day if you're not a professional. You can also take turns with another family member so one could rest while the other is working. Hell, do it in a group of 3-4 and you can share stories about the deceased. Like I said, it's a ritual. Doing it alone would be quite miserable of course.