Yes and that is true for most countries.

It is not true for the United States. The cost varies based on the distance between the shipper and the receiver. Shipping from New York to New Jersey is much less expensive than from New York to San Francisco.

I know, it's just how it works for most countries, because most countries are smaller than the US and often the national post offices have a mandate to treat remote parts the same way as the more accessible parts.

Because the countries are so small? In the USA, you could be shipping 30 miles or 3000 miles (not counting including Alaska and Hawaii).

That's insanely inefficient

The stated goal is often to help the more remote parts, even if it costs more to ship to a small town in Brittany than to Paris.

Yes, we all understand the goal for the national post. USPS charges the same for a first-class letter no matter what and has some flat-rate options based on size. But even they discriminate based on location on most packages. And we're talking about private sellers who are incented to minimize costs, using private shipping companies.

It might be different in the US but in most places I know, the national carrier is cheapest and the private ones like FedEx or TNT are used for special requirements, like faster shipping or special dimensions. There are a few cheap private shipping companies but they are also flat rate.

It's close enough. I'd expect last mile delivery to be the biggest cost driver anyways.