As I think Naomi Wu said, the paper tests are extremely accurate in the lab, the majority of errors come from failure to read the output correctly (misinterpretation or otherwise).
So adding a digital readout that produces unambiguous results justifies the price.
It's easier to have a group of professionals program it correctly once than it is to have someone who only uses these tests at most every 11 months (assuming success) try to read it themselves.
The issue isn't that it's hard to read. The issue is that humans are psychologically conditioned to believe whatever the machine says and not their own eyes.
My wife works in a lab, has a masters in biology and I'm decently scientifically literate and we had a hard time being confident that we were reading the paper strip correctly by ourselves.
Is it a faint line? How strong does it need to be?
Is that a line or is it a smudge?
Did we wait long enough?
Well these online instructions are for a previous model, are they still valid?
It's not easy. But having a calibrated machine tell you "pregnant" or "not pregnant" give a lot more confidence about scheduling a follow-up test with the doctor
So adding a digital readout that produces unambiguous results justifies the price.