Initially, the local Telcos weren’t doing eSims, so you either had to do the physical sim swap or find a suitable eSIM service provider. They’re all doing eSims now, so one option is to put your primary (local) number on the eSIM and free up the physical slot for local sims you pickup along the way.
*BUT* the advantage of eSims is you can get them before you leave the country or even swap over - without needing to go into s physical store etc.
If your using iPhone, here’s some info:
An eSIM is a digital SIM that allows you to activate a mobile data plan from your service provider without having to use a physical nano-SIM. Learn about setting up an eSIM, transferring your SIM, what to do if you can't set one up and how to erase an eSIM if you ever need to.
support.apple.com
I suspect some people don’t even realise they have a dual sim phone because the esim options in settings don’t appear until you load one.
Click through on the page above shows “eSIM carriers”:
Your iPhone XS, iPhone XS Max or iPhone XR, or later, can have two mobile phone plans, one on a nano-SIM card and the other on an eSIM. Find out which wireless network providers in your country or region offer mobile phone plans on an eSIM, activated either by a QR code in a carrier's app or by...
support.apple.com
If you rock up to one of those countries, you’re supposed to be able to purchase some service and scan a QR code to load up the eSIM.
If you’re just after roaming data, TruePhone, Flexiroam (and others) have packages / bundles. They come with an app to manage the eSIM and packages.