Because your drop page needs them. When a drop is published, every product on it is made active in Shopify — otherwise the drop page couldn't be previewed or verified: the buy buttons would point at products your store refuses to serve.
What to do if you don't want them findable
Once you've reviewed your drop page and you're happy with it, go to Shopify and set those products to draft. They'll then only be reachable through the drop page itself — not through your store's search, collections or catalogue.
The email you receive after publishing includes a reminder about this.
Related behaviour worth knowing
- Standalone pushes are different: a product pushed on its own (not part of a drop) arrives in Shopify as a draft, so you can finish descriptions and SEO before making it live. See Will my product be live when I push it to Shopify?
- Adding a draft product to a drop: if a product you've kept as a draft is added to a drop page, publishing that drop makes it active again — the page has to work.
- Editing after publish: pushing edits to an already-pushed product never changes its active/draft status. Whatever you set in Shopify stays as you set it.