Here's why:

* Lack of a mechanism: Alfred Wegener, the scientist who proposed continental drift, couldn't explain *how* the continents moved. He suggested the continents plowed through the ocean floor, but this was scientifically impossible with the understanding of rock strength at the time.

* Lack of supporting evidence: While Wegener presented some evidence like matching coastlines and fossil distributions, the evidence was not conclusive. Geologists couldn't explain the seemingly random placement of continents and the lack of evidence for a massive "tear" in the Earth's crust.

* Opposition from established scientists: Many prominent geologists at the time, who were firmly rooted in the theory of a fixed Earth, vehemently opposed Wegener's ideas. They considered his theory as "unscientific" and lacking proper evidence.

It wasn't until the 1960s that the concept of plate tectonics emerged, providing the missing mechanism and supporting evidence for continental drift. This theory explained how the Earth's crust is divided into plates that move on a semi-molten layer called the mantle. The evidence for plate tectonics, like seafloor spreading and magnetic striping, finally convinced the scientific community of the validity of Wegener's original idea of continental drift.

So, while Wegener's idea was intriguing, it was not widely accepted by geologists during his lifetime. It took decades of further research and new discoveries to finally validate his vision of a dynamic Earth with moving continents.