There has been research into this and it's because unfortunately society has got sicker over the last 5-20 years.
Lots of reasons for this. Long term poor investment in health, Covid and long term affects - we are seeing long Covid and higher rates of ME that was chronically under funded already, waiting lists and poor general access to health care for both physical and mental health. Poor health outcomes overwhelmingly affects areas with high rates of poverty and these areas also tend to have worse access to services many of which were cut over the last 16 years.
Also I have no stats for this, but during the Osborne era and the introduction of UC and PIP many people lost benefits that they were entitled too and never challenged it - the high levels of appeal success backs this up. I suspect many people are now applying again and they are being accepted as it should likely have never been removed in the first place. Of course the usual suspects are all over this demanding that Britain gets back to work, without actually addressing the underlying issues for this.
The number of under 65s struggling with poor health is rising - and it's a threat to the economy.
www.bbc.co.uk
The hostile environment towards people who claim benefits I believe creates deep issues. The negative connotations of "state handouts" doesn't help with this. They are vital in the society that we live in as they either give people the time to get treatment for their condition and to recover without the pressure of finding paid work, or it enables someone who is not able to work, or requires additional income due to the costs of their disability to live as normal a life as possible.
Sanctions have a devastating affect on someone's health. I've watched someone close to me decline into very poor mental health to the point we thought he may have psychosis. It was only once we realised the extreme pressure he was under and difficulties with his housing that we realised what was happening. Amazingly once we managed to get him rehoused (the HA were genuinely great) and he had a regular income without decronian measures being put into place he fully recovered. He was even able to get a part time job that he maintained as he had the basics in place. It wasn't sanction that helped him, but the support of people around him and a secure income from his UC.
I have to deconstruct a lot of the stigma around benefits (please stop calling them state handouts) and taking time away from work if required so that people are actually able to make a better recovery. I believe that has much better outcomes than the stick and carrot approach long term.
I would absolutely love a world that was built more along mutual aid with less state interference, but unfortunately that is a long way off so it is important not to allow welfare to be hollowed out and demonised in the way that it has been.