Everyone is missing a key word in the original post. Solo. That is going to have more to do with how many miles a truck runs than if the company is small or large. There is plenty of freight out there for a team, no matter the size of the carrier. We have one team that has to ask for time off. In all honesty, there's plenty of freight for straights now that most carriers, small and large, have access to. I don't see how a straight could sit much these days unless that truck is hanging out in overly competitive areas where the bidding goes too low, but even then that is more of a problem with vans than straights right now.
The only thing that separates a small carrier from a "large" one would be a direct customer base, and those are dwindling now as more and more shippers are shopping their freight around to multiple carriers instead of giving a contract to one. Because of this, most carriers our size have access to a lot of that freight. With NLM actually talking to smaller carriers as well, a small company with access to NLM, Sylectus, and partner agreements with the other big carriers is on par with most of the carriers who advertise on this site as far as access to freight goes. Yes, you have a couple behemoths with a large customer base, but how do you explain that we have vans who are getting more miles than they did while running for some of those larger carriers? Now that's not always the case. Some people are running their doors off with those larger carriers. There are a lot of dynamics at play other than the size of the carrier. We have vans running a lot of miles and a couple vans that haven't had a lot of miles the last couple weeks. Without going into the reasons for this, let me just say that the disparity in miles between those guys hasn't had much to do with freight availability but more to do with a lot of other factors like not wanting to go to certain areas, sitting too long in one area, or deadheading out of an area too fast and missing freight that a more patient driver would have had, deadheading home a lot, etc.
To sum it up, how many miles you get these days really has less to do with the size of the carrier and more to do with how actively your carrier is looking for loads and how smart you are in the decisions you make regarding which loads you take.