When you have a single store, you have a specific placement assigned by search engines.

These values usually constantly change and get updated.

Multiple stores let's you get multiple placements, with different visitors.

Merchants attempt to have the visitor find them, instead of having multiple locations

that help find more visitors.

All eCommerce platforms are mostly the same. They vary by the way use the software.

They all help you assign products, images, variables, shipping etc.

You create one store, build the content and assign your domain. 

The issue is when you want to duplicate and build an additional store, you are required to set-up a completely different account. You're required to start from the beginning and duplicate all of your work. Your management and  cost has doubled. Different administration, cart settings, customer support etc.. 

Shopify Plus offers up to 10 stores connected, for a fee of $2,000 per month. 

Few merchants would even consider this option.

Perhaps they could develop something custom, but the cost would be very prohibited, and mostly be less then what you'd expect. 

The core for all eCommerce platforms are all the same. A programmer would not have access to redesigning the core structure. 

Since the beginning of eCommerce the evolution has been more about creating a simple user interface. 

The basic format is products, navigation, a shopping cart and the hosted domain. All of the components are connected. It's like driving on the freeway and having an on-ramp and a single off-ramp. You are stuck in your designated lane.

Now, imagine if the products, navigation, and the hosted domain were all allowed to be mixed and matched?

So, first you would add all of your products as a separate component.

You could create any number of different navigation structures. Give each a title.

Open the title and simple "add" the products from your product database.

Now, you'd add your store domain separately and assign one or multiple navigation titles.

You now have the experience of driving on a freeway, getting on, changing lanes and exiting on any off-ramp you like.

 Being that your core components are separate, you no longer have store restrictions. 

With the right partner working for your best interest, it can actually be far less expensive the building individual store accounts.

These are the factors you'd consider:

1. A hosted domain
2. An e-Commerce platform ( either free of fee )
3. Structure management
4. Your administration access being separate

If you created your store for $500, then you can expect to pay about the same each time.

If all of the above are managed within s single initial account, with the hosted domain included, then you can expect to pay an annual fee at a much lower fraction of the costs.

Example: 

Let's say you are paying $50 per month for your domain hosting and eCommerce platform.

That would cost you $600 per year for only 1 store.

Would you be willing to have 10 stores, all connected within a single account for $1,200 per year?

Note: The $1,200 hosted package is a separate requirement

Many eCommerce platforms have you build the front display and your products in the same account. You are then stuck with the options provided or if you have a custom design created. If you visit most Shopify stores, they all sorta look the same. 

You should be able to have the front of your store separate from your product store display.

To duplicate stores, its best they are separately hosted domains and the content is not duplicated.

Then, your domain with your products is separate. Example:

mystuff.com will have a link that connects to shop-mystuff.com

This is repeated 10 different times.

Each of the stores ( mystuff.com ) can then be designed with any software. WordPress, Elementor, etc..

Your sites can change and be updated with being stuck to a specific store platform.

This is just smart long term planning.