Here's why...
š”'Zero' and 'one' are also numbers
So, 'a number of' could mean 'zero' or even 'one'!
Obviously, not conveying the intended message!
"A number of" words/ phrases that you can use instead...
āļøSeveral
āļøNumerous
āļøMany
āļøSome
āļøA few
āļøMultiple
āļøVarious
āļøCountless
Add to the list if you know more...
And, hopefully the expression 'a number of' will become obsoleteāš½
ć³ć”ć³ć