Good question!
Back in the olden days...(and still in houses and top hotels that place much value on impeccable tables and table manners as well as at formal dinners) no one would put proprietory/labelled jars or containers on the table. Everything would be decanted into an appropriate dish with its own spoon, or knife in the case of butter. It's also safer to use a spoon - things either tend to slide or drip off knives or it's awkward to get sticky stuff off them. (The reason for butter presented in curls!)
So you'd serve yourself from the dish and put an appropriately sized spoonful of jam, honey, cream, mustard, relish, butter, mint sauce, mayonnaise, salt etc. on the side of your plate . You'd never use your the cutlery at your table placing. It makes sense because whatever was in the dish didn't get contaminated by whatever you'd had your knife, fork or spoon in, which is good manners and consideration for others at table.
It's also more elegant.
(Plus my mother would have forty fits if you put anything with a label on the table or used your cutlery wrongly! So you just don't! )
Obviously, nowadays we each do as we please when we're alone in the privacy of our own homes. But still, isn't it sort of yukky to open a jam jar and find you left crumbs or a smear of butter in it from the last time...?
