Manufacturers themselves generally don't want to sell directly to consumers: consumers are fickle and need support and have questions and sometimes want refunds or returns and if you sell directly to them, you need to have the staff and policies to deal with all of that. They're also located all over the world, and you might not want to deal with figuring out taxes and duties etc for shipping your product around and figuring out your warranty obligations everywhere you want to sell.

Much easier if you can sell wholesale (sometimes via distributors) to a retailer or network of retailers, and the retailer is responsible for owning the customer relationship, dealing with their part of import/export, local regulations, etc. Retailers are businesses who will buy hundreds of your product at a time, can accept it as palletized freight, and pay you via bank EFTs instead of credit cards.

There are notable exceptions to this model like Amazon's FBA system, but they're the outliers. I'm sure we can all point to inefficiencies in legacy product distribution networks but they solve some real problems.