Theres a huge lack of understand here about the wider demographic of workers
Firstly, how many very young porters do you see, or cleaners in offices? They tend to be much older, in our office probably in their 40s and 50s. I can tell during brief interactions that perhaps they may not have huge cognitive abilities. The work is part time in any case, an hour here, a session there, ideal for somone who might only want to or be able to work part time. These jobs arent being done by motivated and enthusiastic school leavers with their eye on supervising.
And on that note, how many supervisors or managers do you think there are for ever 20 cleaners or porters or supermarket staff? 1, perhaps 2 depending on the set up? You can be as competent, experienced, knowledgeable as you like but 19 out of that 20 looking to be the next manager are going to be disappointed.
Being a supervisor or manager has a completely different skill set to coming in every day, rotating stock, wiping bums, pushing trolleys, its stressful, you need people management skills, which I have found over my career cant really be taught, you can upskill to some degree in that area but you've either got it or you havent. its not for everyone, its draining and more timely. People may not enjoy that or want it.
Many workers may have either undiagnosed or diagnosed learning difficulties, dyspraxia, dyslexia, just lower than average cognition and nothing specific. They're not going to want or be able to get mor and more qualifications or study to achieve something, and thats ok
I really take issue with this idea that someone isnt valuable because they're doing a low skill job, these jobs are valuable and necessary to society, its really prejudice and snobbery about someone working on the shop floor and how they should or could work harder, work smarter, achieve more. Well they have achieved what they want and can and thats ok.
Some of the threads on here are an eye opener about that, countless angst about a child dropping out of college and getting bar work or shop work and its like the child is dying or something the way its spoken about.