once youre big enough its far easier to manage staff who are just at one or two sites all day. its far easier for admin also. obviously losing a big job would hit you hard, but you would also be continually tendering other large contracts. a large company trying to manage literally thousands of domestic customers would not be worth it.
im not saying its easy, but if youve got a lot of drive, a desire to expand and a large business overdraft then commercial only is absolutely the way to go.