It is not that our body "focuses" on alcohol but alcohol being a liquid gets absorbed and metabolized quickly (or first in relation to your question), whereas food needs to be broken down first into pieces by our teeth, then it mixes with saliva and then undergoes digestion in stomach and this process of breaking down of solid food to small absorbable particles takes time, so any thing in liquid form (that could be alcohol, juice etc.) gets absorbed quickly and then metabolized.
Although controversial and the data are limited, but alcohol is known to inhibit the action of a stomach enzyme "pepsin" by precipitating it  and may delay the digestion of 'actual food' thereby its absorption. However, in another animal study  no effect was seen of alcohol on protein digestion 
Because of these factors, it appears that the body "focuses" on alcohol first.
Northrop, J. H. (1946). "Crystallization of Pepsin from Alcohol." J Gen Physiol 30(2): 177-84.
Ugarte, G., C. Castillo, et al. (1978). "Protein digestion and jejunal dipeptidase activity in rats fed a normal protein alcohol diet during 6 months." Digestion 18(3-4): 286-9.