Shopify uses apps too, but the store starts out complete
Shopify stores run on apps as well. What differs is the starting point.
WooCommerce is a plugin that adds a shop to WordPress, which isn’t an ecommerce-first platform. Even basics like payment processing usually come from more plugins, often by different developers, each with its own settings, renewals and compatibility questions.
A Shopify store arrives with the core of an online shop already in place, covering products, checkout, payments, discounts and orders. For anything extra you install an app from the Shopify App Store, where apps go through Shopify’s review. Some features, such as Search & Discovery, Subscriptions and Digital Downloads, are Shopify’s own apps, which keeps the core platform lighter.
A planned migration sorts out what is built in, what needs an app and what needs a different approach. You end up with a simpler setup instead of a copy of every old dependency.