It's not the cheapest, nor is it the most expensive. It's not as powerful as some systems, but it's not weak. It's not the easiest system to work with, but it's also not the hardest.
What it is is right in the goldilocks zone, and it allows businesses to DO BUSINESS, not end up having to worry about or even think about many decisions.
Day-to-day I work across 4 ecommerce platforms and Shopify is the one that doesn't keep anyone awake at night and "just works". Sure there's a ton more stuff some of the other platforms we use can do, but we also have a LOT more meetings, dev tickets and headaches with those platforms.
For like 80%+ of 0 to $50m+ online businesses it is by far the best choice because it means the team can focus on connecting with potential customers and selling stuff and not have to allocate nearly as much time or headspace to the Storefront system.
They even have a warehouse partner that packs and ships for about the same cost as DIY.
How so? Nobody forces small businesses to use Shopify, they use it because it's a good product.
It’s a great choice for a vast number of small companies with other things to do.