GFCI's were slow to be accepted. The opposition came froms a few different directions.
The first was scepticism over whether they really worked, or solved any problem that needed to be addressed. Politics played a role; already the "snub South Africa" movement was getting rolling, and the idea actually originated there. I remember the inventor going around with his daughter; they demonstrated the thing by dropping a plug-in radio into a bathtub with her in it.
There was also opposition from those who favored a different approach: low voltage. The low-voltage folks had just begun to see their products take off when the GFCI came on the scene.
The real debate that held things up was -no real surprise here- the debate regarding GFCI's on ungrounded circuits, perhaps as replacement devices. This brought into the fray all the grounde wire/ no ground wire, to rewire or not, older, smaller boxes, and the fuse vs. circuit breaker debate.
To be fair, the first 20 years of GFCI's featured plenty of unreliable models, and versions that were rather confusing to wire correctly.
It is also fair to say that there were plenty of appliances that leaked enough current to cause a GFCI to trip unnecessarily. Any kind of motor with brushes, any kind of arcing contact - even a low-voltage doorbell button - was likely to trip the GFCI. Plus, there were still plenty of products around (especially lights) that had the neutral bonded to the appliance case.
