In most cities in western / northern Europe, it's completely impossible by now to get a mortgage for a home remotely large enough for a family, even with two factory drone salaries and even if you pay all of your life.

Not really, the problem is that the average standard in a home is quite high and makes the average housing very expensive.

The major expense in home purchase is the purchase of the land, not construction. So rising construction standards are not the prime drivers behind current high prices.

What is “the average standard”?

Noticed how you added "large enough" restriction? Standards are changing, today it is not enough to buy just a house, it should be "large enough".

Everyone who has ever bought a house or flat has an expectation that it will be large enough for their needs - whether that is a single person, a couple or a family with two kids. This is not a new development.

2 adults and 2 children on 16m2 with 2 working salaries. It’s not about changing standards, it’s about families with children needing enough room to have beds for everyone and hopefully still fitting a small sofa. Back in the day, that same family would be able to have twice as big a home with one one working parent, but that was before the whole market started playing chicken to see who could put themselves most in debt to carve out a little place to live.

I somewhat envy that time before the 70s where a family could live on one salary and have a house and car.

Today you can’t even buy a house with 2 salaries. If you are living on one salary you will be struggling and will not be credit worthy. The banks assumes a life-standard to uphold which not everyone can cope with. Even if you can live with less the bank follow it's idea of life-standard.

If you omit the second part of the phrase obviously the meaning changes. The commenter clearly said "large enough for a family".

I think it's a response to house builders building new property with really low floor area - many people don't consider that are sufficient anymore. It's a huge problem in the UK where property is advertised by number of bedrooms and floor area is hard to find - so we get houses with lots of bedrooms, but the bedrooms are tiny, and so the whole downstairs area is also small. Standards aren't changing, houses are.

And the kids get mortgages in their 30s too presumably

Only those who either expect to stay employed in the same geographic area for the remainder of their working life (this has dropped from "almost everybody" to "hardly anybody" where I live) or who simply do not care (I presume that this has stayed constant over generations)

Here in the UK you can port mortgages from one house to another...

(Or at current interest rates let out the old place)

Counterpoint, to take a loan you have to trust the system to both do right by you, and not collapse from under you. It might be difficult now to trust those two things.

What's the downside of having a loan when the system collapses?

Just walk away from the property and there you go. The worse the collapse the easier that is.

People have been calling a property market crash here in the UK for many many years, with others making £100ks out of property over the same period. Anyone that is sage enough to call the housing market should start a private equity company and make billions.