It's not fair, no. You need to get over that, let it go.
Life, isn't fair.
It's not fair that I have hereditary disabilities and chronic health problems, chronic and random acute and severe pain that I have to live with the rest of my (shortened) life.
It's not fair that someone else was born into money, inherited a house and a private income that will see them right for the rest of their days.
Fair is a figment of your imagination and the time you spend worrying about that and stressing about it, is time taken away from enjoying the life you DO have.
But these people who won't work - bearing in mind you need to discount those who can't work, and those claiming UC who are working but for whatever reason will never get a job that takes them out of the eligibility to claim bracket - just think about this for a minute:
Would YOU want to employ these people?
Do you think that people who will actually in the end, work very hard at avoiding a paying job (I've met them, some of them put in a TON of effort to avoid working, its astonishing the lengths they will go to and the stress they cause themselves), would do a good job for you?
Would you trust them in your company, to do their work, not let you down, not cost your company money, not piss off your other employees?
Do you not think that if we could just let go of this toddler-esque 'its not fair' for a minute we could see that its actually cheaper NOT to chase these folks and try to force them into work. Do you know how much the government spends on trying to do this, pretty much the entire of the Job Centres work is this - if you took away 'forcing wholly unsuitable people who do not want to work into jobs they can't do and won't stay in' you'd only need a couple of people to advise on the other benefits and show folks the job listings. Most of it could be done via a website.
The real solution is a basic universal income - enough to live on, so if you don't want to work, ok don't.
However if you're disabled, you get a bit more.
If you want to work - you can then earn even more.
Those who want to work and get fulfillment out of working would work. Those employers who need people to do grotty jobs would HAVE to pay people properly for that work. You would end the toxic work culture that sees people expected to be at their desks hours after their salaried hours are over. You would stop people overworking to the point of burn out then going 'on the sick', you would no longer have horrible sickness policies in workplaces that force people to come to work when they're unwell.
People would work a little less, but they'd live better, be healthier, there'd be more competent people with spare time to volunteer for charities (many of whom suffer from the grim fact that volunteers tend to be lacking skills/useful experience because teh volunteer pool is small).
But it will never ever happen until people can let go of 'its not fair'.