ELI5: Why are nulls not ignored by default?

Every time I've tested a SQL query and realized that some null somewhere broke my CONCAT statement, or run an R script and realized that I forgot to add "na.rm = TRUE" to a function somewhere, I wonder what was going through the development team's minds when they decided to build these tools these ways.

Why isn't ignoring nulls the default behavior?

Genuinely curious if there's a logic to this that I haven't considered.

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