That is because the computer has the ability to learn parameters to deal with small changes in what it sees and makes adjustments so that engind still runs and improves over a bit of time. (I can't remember the term but a computer guy would know it)
All an engine light is, is and indicator of a parameter change.
Engine lights are properly called MIL or Malfunction Indicator Light.
Most cars today have a computer that operates the engine as well as the trans and often has sensors in other drive components too PCM all in one unit. (powertrain control module)
All these systems have been more and more consolidated through the years and the systems more reliable and easier to troubleshoot for mechanics.
Any good shop has thousands of dollars in scanner tools and software to
read what a cars computer sees.
Typical 20k plus for the average shop. Last shop I worked had about 90k
in.several scanners because they worked on all things, Yugos to semi trucks.
Key word “for mechanics”.