Are there reasons for not storing boolean values in SQL as bit data types?

Question

Are there reasons for not storing boolean values in SQL as bit data types without NULL? I see them often stored as integers without constraints to limit values to 0 and 1,

Answer 1

I see them often stored as integers without constraints to limit values to 0 and 1, and as strings with things like T/F, True/False, yes/no, etc., again without constraints. Isn't it better to store them as bits and not have to worry about additional constraints?

Yes!

What am I missing here?

Actually it should be "what am I NOT missing here?" and the answer would be: common sense.