Why did most marriages lasted in the old days?

Not true. Women had been fighting feircely for women's rights and independence for a good 100 years or so now, going back to the women's suffrage movements of the 1910s. They finally started succeeding when WW1 killed so many men to where women greatly outnumbered men for a while, which in turn made women so desperate for male companionship, that they started going to extreme lengths, thus introducing flapper girls. They'd already been fighting for their rights, but they finally succeeded then.