In the story I want to tell, it's a thousand years in the future and Mars has been terraformed into a forest world (something like the forest-moon of Endor). It's settled in a few small towns and mostly populated by a rugged group of lumberjack types. Every year (Martian year) the logging crews go out in the fall, cut timber all winter, and in the spring the logs are shipped back to earth to be made into furniture, paper, etc. Earth is densely populated, urban, with all the modern conveniences, but has few large forests and is unwilling to harvest them.
My worldbuilding problem is that I want Mars to be a kind of hinterland with an uncivilized, frontier character. But if people have the technology to transport millions of pounds of lumber off Mars and land it safely on Earth, via antigravity drives or something, then Mars would not remain sparsely populated for long. Billions would move there and build giant cities complete with shopping malls and everything else. Moreover, if it were easy to transport heavy loads from Earth to Mars, the lumberjacks themselves would probably be replaced by heavy machinery such as real loggers use in the 21st century.
Instead, I want it to be very difficult and expensive for freight to get from Earth to Mars, so it'll mostly just be loggers with hand tools going that way each autumn, but very easy for heavy freight to be transported from Mars to Earth. The not-so-subtle metaphor is that Earth is "downstream" from Mars, and the logs are being "floated downriver" as in the olden days (on Earth) when there were annual riverdrives from logging operations in the deep woods downriver to the mills.
What's a plausible science-fiction explanation for this scenario? I'm defining "plausible" as meaning that the explanation must be internally consistent, i.e. not creating side effects such as godlike technological powers. Bonus points if your explanation also helps explain how Mars was terraformed.