Because cooking has turned into something social somehow, people don’t want to be isolated in the kitchen any more.
But in the past, someone walking into the kitchen while you were cooking would probably have been akin to them walking in on you in the toilet (“What!? No, I don’t want them to see the dinner until it’s actually done!”).
This comment boggles the mind. I would wager that probably for thousands of years, cooking has been a communal (if perhaps gendered, good riddance) affair, and only with the advent of the unemployed housewife of the 50s suddenly the kitchen is seen as this private affair.
But i guess i'm the wrong person to be commenting, because generally i'm no fan of all this extreme individualism :)
Depends on how far in the past, and where.
In the USSR, kitchen has always been the place where people would end up spending a long time talking about whatever.
There is even a phrase "kitchen conversations", which would mean talking politics (without regard to what the Party says).
And, of course, the Kitchen was the social hub in the communal flats (living with roommates, Soviet-style). There usually would be no common area in a communal flat other than the kitchen.