Supply and demmand. That’s all. As long as there are more people wanting the job than there are vacancies the pay will be low. If you are recruiting drivers then you will only offer the least amount that you can get away with - why would you pay more?
I was a TM on own account back in the day when the T&G ruled in Birmingham. The first thing I did when I started was to stop the Saturday mornings - four hours at time and a half to wash their trucks - dream on. On the other hand I defended the drivers against the general impression at board level that they were really just labourers.
The drivers there were on trip and finish for the week. So they would roll in on Friday morning and hang around fo no good reason. This upset the factory workers because they only saw them when they were standing around drinking tea. I stopped most of the overtime too - the rule was that they couldn’t claim OT on a day when they had a night out. My reasoning was that there was no reason for them to work it, apart from the odd half hour to get to the digs (no sleeper cabs then).
This was 30 years ago and, just as now, drivers were mostly interested in the “take home”. Since most drivers work long hours the hourly rate could be low while the “take home” was (and is) high. Applying for a job as a manager I would look at the whole package - wages, pension, sick pay, holidays, bonus, severance et al. You see it on here all the time “I take home £600 a week” The fact that this is for 80 hours and includes six nights out seems not to matter - only the “take home”, and of course a nice truck.