why did old "antique" dressers have drawers with locks?

Interesting question.

Somebody else said to keep honest people honest and I think that is a good clue. In the 1800-to mid 1920 lots of folks had servants. Locking a dresser drawer would be a good way to keep a house servant from helping themselves to silk hankies, stockings as well as other expensive items like jewelry, and wallets.

Antique Dressers

It would be a shame to put a lock on a dresser. If handels line up perhaps a bar running through handels and secured through under side to the back side.,would work. This is how file cabinet locks work. Catching her with" fake cosmetics" to teach a lesson may work. Replace something she likes with food die, fabric die or even something like pepper water.But first put up sign saying this is your "Private drawer and Stay Out." Meanwhile help her earn and buy some for herself so she can learn about the cost of items she likes.

These were built in the days when most people regularly left their front doors unlocked - it was a different society then. Parents used the locked drawers for privacy for documents, and they served their purpose within the family. It kept the snooping by servants as well as children under control. One of the duties of the 'Master of the Household', the top servant in large estates was the holder of all household keys - it was considered an honor.

Most people had less furniture than we have, and the locked drawers were only used in high-end furniture. The keys were not transferable to other furniture sets, although the pattern of the tumblers would make them easily picked by today's lock standards - even house keys were of that pattern for hundreds of years.

There is an old saying, "locks keep out honest people". And more than underwear were kept in "drawers".

So I can prove how old it is when I sell it for 4xs. The original purchase price

To keep the pantie bandits at bay.