Employers pay the lowest they can get away with. Businesses are about making money for their owners/shareholders. Higher wages means less profit in the immediate term, and businesses chiefly look at the immediate future.
I worked for a company that was privately owned by descendants of the founder. They didn't work for the company, but they took the profits so they had a comfortable life without having to work themselves. The thing was, with every generation there are more people expecting to be supported. Their individual percentage share of ownership was lower, but they demanded the same return. Hence the company got squeezed until it collapsed.
The other big reason is cheap labour from abroad. The shortage of British workers willing to do the job for the wages offered means firms import people who are willing to do it. Which means wages are lower, British people cannot afford to do the jobs and more immigration is needed. Immigration is the real cause of the cost of living crisis. It drives up house prices and keeps wages low. Cut the problem off at the source, remove anyone who has arrived in the last 30 years (and their children and grandchildren), confiscate their property and after the short-term carnage we would have a much better society with plenty of cheap housing and employers having to pay higher wages.
That's the real solution. Drastic yes, inhuman certainly, but that's the basic problem: a good living standard for one person means a much lower living standard for several others. Wages are low because workers are feeding money to the few at the top. Millions have to be screwed so thousands live well. The choice is, do we want the country as a whole to be in the "elite" in global terms - which means being comfortable screwing over most of the rest of the world - or do we want to act with morals but be consigned to remain forever poorer?
There's no ethical solution that enables everyone to live well. Wealth is comparative, for one person to feel well-off or comfortable, many more have to feel poor.