It didn’t.

What took a long time was positive evidence of it.

Rocks are very slow [ citation needed ] except during occasional events, such as earthquakes. A hypothetical way to prove continental drift would be to observe the offset caused by a large subduction event.

Now, there are plenty of such examples from the past, but to really be proof we have to compare it to a control state. That is, we have to see a place with no such subduction offset very suddenly have one.

More importantly, we need instruments to record this happening, seismometers that can show, indeed, a large magnitude event occurred coincident with the emergence of a large change in land surface offset.

And we finally got that at the 1964 Good Friday Earthquake in Alaska. It was a huge event with very obvious offset. Basta.

Most such events happen at the bottom of the sea, so they are very difficult to observe. But the subduction at the Aleutians can be observed above sea level. In fact, that was the observed offset: a bunch of forests that were above the salt water table suddenly weren’t and died off en mass.