Electro-mechanical devices fail at random, arbitrary, and capricious times.
The most frequent reason for most failures is 'just because'.
Your specific failure is most likely caused by an advanced scientific principle called ...
... 'bad luck'.
If you want a really substantial lesson how this this works (or more precisely how this stops working) own an older used automobile.
Extended warranty:
Some manufacturers offer extended warranties, also known as service contracts. For a modest pre-payment, the manufacturer agrees to service their product for an additional period of time -- to repair or replace defects in Materials or Workmanship, and possibly even more, for an additional period. In some cases, the service contract covers additional items beyond defects in materials or workmanship. In some cases, there is a copayment required to obtain this service.
Some users will have No claims during this period. This "insurance effect" allows the manufacturer to keep the price of this service contract relatively low. You generally can not sign up later, because then only owners with problems would sign up, after they discovered an issue.
The MacBook Pro is a lightweight, portable computer that can run on batteries. Being portable, it can easily be subjected to multi-G forces daily, just by being moved about in a completely ordinary way. This is extremely stressful to electro-mechanical equipment. The display is made of glass, the internals are very likely to die if water is spilled on the keyboard.
Because of this, you should ALWAYS purchase the extended warranty coverage for such a portable device, regardless of whether you intend to move it about.
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If you made the decision to NOT pay for the AppleCare extended warranty, you made a decision (wittingly or unwittingly) to bear the cost of repairs during the extended warranty period yourself.