A number that multiplies a variable is a coefficient. Coefficients therefore do not exist in arithmetic because there are no variables. Algebraic parenthesis containing unlike variables cannot be added in order to be fully simplified, therefore the distributive property is used to multiply the parenthesis and consolidate all like terms in the expression bringing it to its most simplified form, so that it can be solved for a variable. When a number is juxtaposed to an algebraic parenthesis the result of the term it is part of is used to distribute multiplication over the variables in the parenthesis creating variable/coefficient pairs. These variable/coefficient pairs are the simplified terms of the parenthesis. At this point the expression is fully simplified.
In an arithmetic expression there are no variables, and therefore the parenthesis can be fully resolved to a single number which makes distribution completely unnecessary. It is simply extra steps that serve no purpose since distribution done correctly yields exactly the same results as calculating the operation in the parenthesis and multiplying the single number results without distribution!