They are. Personal trainers typically work at gyms and are 'for hire'. Dietary advisors are probably less common, but I was just looking for a few example fields for things you could learn from the library, for which I think that fits the bill.
You're not wrong that there are barriers to these jobs, but that's true of anything. As IT professionals, we're used to seeing "minimum 10 years practical experience + portfolio + FizzBuzz tests" as job requirements, but almost every job has some barrier to entry, whether it be related experience, references or what have you.
Construction jobs (in boom times) are more plentiful, but require physical fitness, tools and the ability to be handy. Pizza delivery generally requires a vehicle, insurance, a clean driving record, etc.
There is no magical place that people can go to become employed, but I tried to pick fields that had learnable skill sets or (in the case of the first few, definitely sales) jobs where one's pluck and enthusiasm could go a long way towards landing. I've worked with a LOT of salespeople over the years, and it's all personality-based at the entry levels, if you can convince the person to give you the job, you can get the job. It isn't until one tries to progress in sales that past performance even becomes that big a deal.