Why were scientists surprised when they first discovered the existence of planets with Jupiter-like masses orbiting close to their stars (the "hot Jupiters")

The Jupiter-like masses or hot Jupiters are gas giant exoplanets that are found outside the solar system.

Formerly, scientists used to rely on planetary formation theories which stated that the hot Jupiters are only found at a very large distance from the stars. Later, the discovery of hot-Jupiters came as a surprise to astronomers because they are found so close to their stars.