For two reasons,
1. CD players have over the years become a lot better at dealing with scratches and other types of read errors. They are, simply put, decently good at overlooking optical issues.
2. The audio stream format on the disc, PCM, is deliberately designed to allow a misread here and there, and still produce sound that doesn’t get interrupted. It both has a massive amount of data that can be used to recreate data that went missing in the stream and, to be frank, an excess amount of data to begin with so that it’s not really the end of the world if a small amount goes missing.
CDs have extra data encoded on them. This allows the player to calculate what data it has not been able to read if it’s obscured by a scratch.
All the data on the disc is also re-arranged in a way that is best able to cope with intermittent read errors caused by scratches, dust, etc.
The system is called “Cross-interleaved Reed–Solomon coding” [wiki page](https://en.wikipedia.org/wiki/Cross-interleaved_Reed%E2%80%93Solomon_coding)
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