Learn English – Why do people who find it hard to hear say they are “hard of hearing”

It's a metaphorical usage, so there doesn't have to be a direct link between people and pushing the buttons they don't have.

Dictionary.com indicates the phrase originated in 1920s America, when domestic electricity was being installed on a massive scale. The ability to push a button to turn something on had a big impact on lifestyle, and the metaphor spilled over into other things which have an immediate effect — like being able to trigger a specific emotion.

During the 1920s the spread of technology transformed the way average Americans lived their daily lives. In 1920 only 34.7 percent of American dwellings had electricity; by 1930 67.9 percent had electric power. In the cities the growth was even more dramatic: 84.8 percent of all urban homes were wired for electricity by 1930, compared to only 47.4 percent a decade earlier.

At the turn of the century, families with a comfortable income depended on servants, hired labor, and delivery men to support their day-to-day lives. The new technology available in the 1920s—combined with a diminishing supply of people willing to work as servants—caused more and more middle-class fami-lies to do their own housework. By 1926 80 percent of American homes with incomes more than $3,000 had vacuum cleaners and washing machines.

American Decades © The Gale Group Inc

Searching Google books, I find that what the phrase originally meant in the 17th and 18th centuries was that "A loves B just as much as B loves A"; the amount of love is balanced, so there is no love lost. In other words, unrequited love was considered to be "lost". This could be used to say they both love each other equally, or they both hate each other equally. The idiom has now come to mean only the second possibility.

From this 1754 English-Danish dictionary we have a translation:

ieg elsker dig ikke meere end du elsker mig
(literally: I love you no more than you love me)

(1712):

You must know, Sir, I love Prudence, my Lady Laycock's Woman, and I believe there's no Love lost between us, nor do I know how soon we may exchange our Persons for better and for worse.

(1645):

He hates the Council here, and I find plainly there is no love lost; they fear he will seize on the Prince, and he, that they will take him.

John Dryden (1712):

— By Bottle and by Butt I love thee. In witness whereof I drink soundly.
— Your Grace shall find there's no love lost. For I will pledge you soundly.

There's also a translation of the expression in a 1732 Irish-English dictionary, but I don't know Gaelic.