Some people don't know what a screwdriver is nor what to do with it if they have one.Costs a lot to have that employee available, even for small jobs. Between wages/taxes/benefits, etc ... may cost $50-100 per hour each employee. They've gotta make that back somewhere. Little jobs are a quick little bump to the bottom line.
And ... some people can't twist their bodies into the positions you need to install filters and such, so they pay the premium.
.