In 1970, the cost of a 1st class postage stamp was 6 cents. In January 2023, that price will increase to 63 cents, more than a 10 fold increase over 50 years.
However, that is not the worst instance of inflation. In 1970, Medicare cost senior citizens $5.30 per month for part B premiums. Today, those premiums cost $170.10 per month. That is an increase of 32 fold.
The problem with USPS costs is that much of the cost of mail delivery used to be covered largely by the segment of mails considered to be Direct Mail. That included things like magazines, catalogs, and advertisements. For example, Publishers Clearing House used to send one of their advertising packages to every household in the USA. They expected fewer than 1% of households to respond, with everything else going in the trash or recycle bin. That huge volume of mail covered a significant portion of the operating costs of the USPS. Today, there are still a few such mailing such as local grocery store ads and clipper magazines. However, most direct mail sent on a national scale is highly targeted to those from whom the advertisers expect to get a greater percentage of response. Advertisers now use data collected by Google, Facebook, Instagram, etc. to target email and pop-up ad campaigns to those who have shown interest in specific items or topics. These electronic ads are significantly less expensive than the costs of printing and mailing. Thus, the unwanted paper in your mailbox has decreased; unwanted phone calls and emails have increased. That change in advertiser behavior has significantly impacted the income stream of USPS. Today the cost of mail delivery for letters and packages has to more closely correspond with the actual cost of delivery.