I used to work for a big online recruitment company.

When they started their business, they used to focus on smaller clients (i.e. lots and lots of small clients.)

After about three years of this, they realised it wasn't working. The amount of effort they had to put in for small returns was actually killing the company (they had to consider liquidation.)

They knew something drastic was required so they scrapped the "small job" idea and instead focussed on large corporate clients.

The change was huge: they went from losing money to pulling in hundreds of thousands per month within a few years.

It's no coincidence most jobsites are aimed at big corporate users rather than the little shop down the road...

EDIT: Also, large customers are much slower to change supplier. The little guy - it's in his interest to shop around.