Many of these thermal and carbon transfer receipt printers have poor ink/print life. I doubt it was done on purpose as most of these systems are sold by 3rd parties to retailers. I'm sure the issue has been raised but then they willing thought to themselves, yeah actually this benefits us, let's just "pretend to ignore" the issue.

More modern retailers are offering receipt-email options which is the option I choose if available, that way I have a "permanent" record of the transaction. I recently did some old taxes from 7 years ago and this feature was invaluable as most online portals no longer offered the records.

Not likely. It's just a technical limitation of thermal paper. That's the trade-off for cheap, tiny form factor, fast, and low maintenance printing.

The other answers mentioned _what_ happened. In terms of next steps:

(1) Generally, receipts should be scanned (and perhaps re-printed, depending on your needs) for any sort of conservation effort. The heat from scanning (not in any modern tech, just as an FYI so you can decide for yourself) can cause the same degredation. It doesn't necessarily take a long time either. If you ever order a pizza where the driver tucked the receipt in the box you'll also notice that chunk of the receipt is illegible.

(2) If it's partially visible in its current state, you can probably get away with increasing the contrast and applying a decent OCR to the result. You'll get some hallucinations, but if you fill in the most likely characters conforming to the grammar of a typical receipt you're likely to be in the right ballpark (if you need a particular warranty code or something you might have to manually try a few options for particularlly blurry letters). Pair that with a photo of the receipt in its current state for any distrusting shopkeeps.

It's thermal printing, they heat the paper to turn it black, but if you store it somewhere warm the chemical reaction can reverse.

The fading of receipt is a common issue with thermal paper and I do not believe that it is done on purpose

Receipts are commonly printed on thermal transfer spools to avoid the maintenance needed for printing with ink but this process is not as durable as using ink. Decide for yourself if this decision is made due to cost or a conspiracy.

It usually disappears way faster than that, often ater a year or two. Could be useful to photocopy. However most of warranties those days are not really longer than this ¯\_(ツ)_/¯