"chosen"? Lol! They can't have families because they can't afford them. Council housing has fallen since the seventies from 30% to less than 10...Manufacturing jobs are down 600,000 in the last ten years alone: the young are either on minimum income jobs, zero hours contracts or in the gig economy.
There's no work security & no domestic housing security...a massive decline in public transport and with rising costs on everything.
Massive immigration exacerbates all these issues as above: it's not about making up for a natural shortfall because the working classes have somehow "chosen" to have fewer children.