Rent as a percentage of income is remarkably steady historically because it’s always as high as the market will bear. That’s the rationale behind Georgist Land Value Taxes. You can pay it to the government and the landowner or the landowner, the amount of rent will be the same. Food has gotten cheaper as well as tastier and higher quality over time. The proportion of income spent on food has been dropping for well over 100 years.

This is a major factor. Also, day jobs were a lot more chill. Writers still complained about having to go to an office job, but you could use the copious downtime on some of the work. You wouldn't want to do hardcore creative first-draft writing at your office job, but you could edit for typos and do background reading.

These days, so many fascistic surveillance technologies have been deployed to squeeze the downtime out of existence for most jobs. You could have a 1950s day job (well, if you were middle class) and be a writer, but you can't really have a 2020s day job and be a writer, because jobs are so much more stressful.