In SQL as you've said, nullability is explicit. It's arguably the wrong way around (i.e. NOT NULL rather than NULLABLE), but it is explicit. I feel the issue comes from the intersection of languages without explicit nullability and their data storage techs; removing that explicit typing from SQL doesn't fix the issue.
(I feel you agree with this btw, just being explicit)
I finally made an account just to respond to this, I hope you don't find that too aggressive a move.
Null is a perfectly valid value for data, and should be treated as such. A default value (e.g. -1 for a Boolean or an empty for a string) can make your system appear to work where NULL would introduce a runtime error, but that doesn't mean your system is performing as expected, it just makes it quieter.
I know it's tempting to brush NULL under the rug, but nothing is just as valid a state for data as something, and systems should be written generally to accommodate this.
(I feel you agree with this btw, just being explicit)