If it’s so simple, why didn’t you do it and save $2,000? Part of that price is uncertainty due to scheduling/coordinating with the siding contractor and utility.
Everything after the meter, including grounding conductors, are premises wiring aka your responsibility.
Having your electrical service properly grounded sure beats being electrocuted.
I manage electricians, and my jobs get charged $110/hr for a journeyman in a service van.
There are some jobs that I can do, but I hire someone else to do anyway.
Getting the work done properly was important to me. After the replacement, the random occasional 2-3 second power outages went away and it looks great.
My point was mostly to concur with parent that often you do incur unexpected work when updating legacy electrical, and that adds a bit of cost. To a homeowner, a box swap seems simple but can wind up costing thousands more than you expect.
Think of the old "I could write twitter in a weekend" adage. Sure it seems simple at first glance, but once you get into it it's far more complex.
A layman would think "It's a plastic box with a couple of wires in, surely it can't cost more than $200" and take more than an hour".
Most residential wiring really is as simple as it appears at first glance.
The problem is that there are a few cases where it isn't, and the issue is being able to know when that's true. This is where the skills and experience come into play.
In case I need to cite some authority, I've been wiring my own homes (with permits) for > 25 years, and was licensed by New Mexico to install my own 6.7kW solar array a couple of years ago. I'm not an electrician, however.
UK note: under "Part P" rules, it is significantly harder to legally do your own electrical work. https://www.electricalsafetyfirst.org.uk/find-an-electrician...
He probably just checked to make sure you strapped the NM cable within 8-12” of the box (depending on if you have cable clamps or not) and then a strap every 54”. If you get the small details right they won’t be so harsh while inspecting.
If you are careful and follow the rules, it’s pretty straightforward to wire branch circuits in a house. Grounding and bonding a service entrance panelboard to ground rods/natural gas piping/water piping is not as straightforward as it seems.