Companies got used to buying what they need when they need it - the huge pool of cheap EU labour fuelled that. (Take on a bright, fit, ambitious chap who's in GB for two years to perfect his language skills and get a bit of experience but going back to his EU country to be a doctor or an engineer). Ideal labour.
Firms don't want to train people - and it's not worth their while either. People stay two - max three years.
And if they take on people who are useless, wasters, piss-takers - they can't get rid of them so they want an easier option.
Youngsters don't do part time jobs any more - the law and other things led to a decrease in that so the average 18 year old is totally unskilled. (I'd worked since I was 12 in shops before I went to uni).
Benefits are too high and too easy. People will disagree, Fair enough. But if you can take home the same per month on UC etc why the fuck wd you work for it??
All the points already mentioned - inheritance has meant the older - but not too old have big chunks of money from their deceased parents so can swan about playing golf and going on cruises.
Work is also shit - the general public treat the people who work like utter scum. "Complaints" as soon as you don't get what you want. Swearing, shouting, abusing call centre staff, delivery drivers, doctors receptionists, NHS staff, supermarket workers, teachers, basically anyone who doesn't give you what you want when you want it... No wonder no-one works.