Dave Plowman (News) formulated the question :
They were often rented, because they were so expensive and because
there would then be a cost free ready repair option, when as they often
did, they broke down or needed adjustment.

And the rental company supplying a social service, then? ;-)

No different from having a service contract on your heating system. Long
term, the supplier always wins. And by a large margin.

Of course the supplier wins, they are never charities - they are a
business and need to make a profit.

Back in the day, many companies were set up as a source to rent TV's
and it was a sensible option to rent one.