Some theorists feel that the gas needed for Core Accretion may not linger in the disk long enough.

In the theory of ‘Gravitational Instability’, gravity causes the disk of gas and dust to collapse into dense clouds, which shrink and form solid cores within a few thousand years. The rest of the cloud contracting to form the gas giant around the core could take less than a million years.

If more giant extrasolar gas planets continue to be found, this would imply that they regularly win the race against this erosion of the disk.