Ok, I see these kind of posts so often.
From your job title, I presume you are employed? Do you know that it costs your employer way more to employ you than they pay you hourly? They pay into your pension, NI, holiday, public liability insurance and provided you with everything you needed to do the job and advertise to bring in the clients for your company.
A cleaner is self employed. So we don’t have anyone buying everything we need for the job. I’m a cleaner. Year to date, my costs are 30% of my turnover. Out of my remaining 70%, I need to take out my pension. No one else contributes to that. Holiday pay for an employed person is 12.07% of your income.
So, that self employed cleaner who is charging £20. Let’s take off 30% for her overheads, that leaves £14. They’ll get no holiday pay. No pension contributions.
Anyone paying their cleaners £15, after overheads that cleaner is making £10.50 per hour. NMW is over £12/hr. Plus an employee would get all the above mentioned benefits.
Do you question, when eating out, why a meal costs more than if you prepared it yourself?
So, in answer to your question, that’s why they charge what they charge.