As a Shopify Partner, you can create multiple partner Accounts and multiple stores.
I wasn't sure the point of this as each store is already a separate entity. I wasn't sure when I should create a store in a different Partner Account or what was the reason…
So I asked Shopify support what's the point of having multiple Partner account if you can already have multiple stores within 1 Shopify Partner account?
In regards to your question about having multiple partner accounts, this is not needed for one partner organization as you can create multiple stores under one account as you mentioned. One reason why a partner may create a second account is if they are a part of two separate companies.
The answer is pretty clear to me. Just another way to further organize your Shopify account 👍