Other commenterd have described the role of the deductible but there's one point I would like to add.

It's important to remember that insurance companies are not in the business of providing healthcare or access to healthcare. They are in the business of selling you insurance to deal with the cost of your healthcare. A lot of the things they do make more sense within this framework. Anything they can do to transfer costs to you improves their profits and deductibles are part of that model.

This is one of the reasons why the US healthcare system is so problematic and results in so many people not obtaining the care they need or going broke in the process. The entire thing hinges on private companies that are not actually in the business of providing care and are not driven by patient outcomes. They're financial service providers.