Minimum wage has gone up but wages have stagnated (or in real terms declined) in more skilled roles, so work doesn't pay anymore.
Homes are over valued so people approaching retirement falsely believe they are financially secure enough to take early retirement, or some are genuinely well off with property and other assets and a gold plated pension so can retire early.
Childcare is extortionate, so stops some people working.
Long term sickness due to a failing health care system.
Falling birthrate and large generation of boomers dying out while the other large generation are stuck with high childcare abd high rent, so are better iff one parent not working due to having children.
employers taking the piss with wages and job conditions that nobody in their right mind would accept.
Lots of job positions are fake online.
Oh and brexit, and the fact that it is actually quite shit for families in the UK, so international workers go home to raise kids, which is what has happened with lots of my friends.
It's not millions of people on benefits, but I don't blame people for staying on benefits if working is not benefiting the worker financially.