I think there are very few people who make the deliberate choice to exist on benefits - and it is existing, not living. As those people who have personal experience of having to live on benefits or who have friends and relatives in that situation know, immense pressure is put on people to find jobs - even in areas where jobs are scarce. They can't just rock up at a Job Centre (or whatever they call them now) and demand all sorts of benefits.
As others have said, almost everybody who needs to work to obtain an income is at risk of finding themselves in the position of having to claim benefits. Redundancy or illness, especially for people who were already only just managing and who have little or no savings, can so easily lead to homelessness, hunger and reliance on foodbanks. I am so aware how lucky we have been never to have faced such an awful situation. It's a pity other people can't count their blessings instead of criticising those who have been less fortunate.
Although this is about Universal Credit, the dire housing situation compounds the problems for low income families. The right to buy policy has been a disaster and the increasing prevalence of second homes adds to the problem. They may only be occupied for a few months, or less, a year. Meanwhile, the influx of second home buyers in more and more areas of the country means that prices have rocketed and locals can no longer afford to buy. On top of that, the decrease in local permanent residency has resulted in schools closing and other services being reduced or dropped altogether.
Local councils are considering measures to reverse this trend. In 2017 Yorkshire proposed a 500% rise in council tax for second home owners. There are similar problems in Cornwall, Devon, the Lake District and even less "touristy" areas, so these areas have either introduced or are considering introducing measures to prevent this. I think it right and necessary.
As for saying that anybody who cannot afford to rent a room (£100-150 in London) should live with their parents, well this might work as a very temporary measure but how can it possibly be a permanent solution.