Disposable razor blades are expensive and they usually need to be replaced after 4-5 shaves. Now, in the olden days men used special leather strips to sharpen those old-fashioned straight razors nowadays only barbers still seem to be using. These maintenance skills seem to have been lost over time leading to the current business model that’s quite similar to the one for inkjet printers: The actual product is sold at a bargain price, sometimes even at a loss, while the consumables needed for using the product (in this case ink cartridges) are high-margin and need to be replaced often.
There’s now reason however why you shouldn’t be using the traditional method for disposable razors as well in order to drastically improve their lifespan. You don’t need one of those leather strips for that. An old piece of jeans cloth / canvas will do as well! Just move the razor in the opposite direction across the cloth for a similar effect. An even better and easier method is using the skin on your lower arm for this (leather being nothing else but processed and tanned skin after all).
The process is described in more detail in these 2 articles (including short how-to videos):