i think not wanting children because it will ‘compromise their lifestyle’ is a fair enough reason.
In some parts of the country affording a big enough flat or house is already a problem. Then of course there’s the childcare cost.
I think a lot of adults don’t want to have to live in overcrowded housing, never be able to buy, not be able to afford luxuries etc to enable them to have a child.
Mumsnet is awful at this puritan ‘oh but you should be miserably poor despite working full time if you want a family’. Well - people don’t want that.
Id also say - the guy on £53k in London. After his loans etc he will be on ~£3k a month. Nursery will cost £2k. Rent probably similar. You start to see the problem.