In our society gender roles are strictly enforced and policed. It has gotten better during the last few decades (though there have also been some regressions) but it’s still pretty bad.
I'd say it's simply because it's a crappy, low-paying, exhausting job with too many working hours, which not many people want. Men usually get such jobs.
What’s your alternative explanation?
The real question is, though, why don't the women get/take such jobs. I think the answer is a mixture of the following: (1) they are worse at such jobs than men (physically weaker and menstruating, which I assume might matter for a job like truck-driving), (2) (I assume) women get more government help, because they are more often (single) mothers and (3) women can play on other qualities (more social, better caregivers, more attractive, less dangerous) that allows them to get other jobs (nanny, waitress, secretary, ...).
You reasons are pretty bullshitty, so I don’t think I ever want to talk to you again. Bye!
I would consider the culture of working oneself to death generally harmful and strictly policed gender roles can play a very dangerous and enforcing role there.
On a side note, you aren't helping the image of feminism by bringing up MRAs out of nowhere just to deliberately present the worlds laziest strawman on their behalf, so you can dismiss it.
I'd scale it back, and draw the conclusions more conservatively. Along the lines of 'employment statistics don't necessarily imply discrimination'. Just because twitter's board is mostly male, doesn't necessarily mean that being male was a requirement. No one would argue that truck drivers are mostly men due to hiring policies.