Why the

It was perfectly normal at the time.
A lot of good work was done by the Spastic Society.
Why the
This horrified me at the time. A lot of British content appeared on Australian TV and I'd often sit and watch with my parents. I wouldn't stay in the room when this was on.
Was it really acceptable, even in the 70s?
(I'm not saying Australian TV is perfect.)
And it wasn't me that did it.I should have quoted @Dirk. I have never seen polio conflated with cerebral palsy before, and it wasn't you who did it.
Dymo tape labels. Does anyone still use a Dymo embossed printer? It was a cutting edge of 1970s drawer administration.
Some kids who'd had polio did wear callipers and any kid wearing a caliper could be called a 'spastic'.
Kids can be cruel.
Apropos polio. It was quite prevalent back in the 50s. Very few classes in our primary school without a kid who'd been in an iron lung and come out with a calliper.