Apple apparently felt comfortable enough with the eSIM situation in the US to drop legacy-SIM already. The fact that they couldn't do this worldwide yet is because, as you say, eSIM availability is still spotty around the world.

However, the fact that they're moving to eSIM-only is a huge flashing warning to telcos around the world that the time to sort out their eSIM support is now. Otherwise, they'll soon be chasing away their affluent iPhone users.

I think the transition will now proceed pretty quickly. Physical SIMs have only continued on due to market inertia.

In a few years we'll look back and think "remember when SIM cards were physical objects... that was weird wasn't it?"

So dropping the SIM in the US is more a consumer hostile move to save a few cents and force them to use the tech Apple wants you to use then anything else.

They can't do that in many other countries as neither carrier nor population where okay with accepting not having a SIM slot.

eSIM is easily usable in the EU many people still insist on using physical sim cards for various reasons, similar "unlocked" phones are the standard in many EU countries. I'm not even sure it's legal to sell carrier locked phones in all EU countries, I think it isn't at least in some.

Before you had to find an operator kiosk at the airport and negotiate with someone there who might or might not speak a language you speak to try to get a pre-paid vaguely firing your need if one exists. Now you can just pre-buy in app before your flight and everything pretty much just works.