Entity (Lavos Disposal)
The answer lies within the Entity's power. The Entity was able to create Gates, but if it fought Lavos by that time, it had lost. The party remark that the Entity is dying, and that the Gates can be compared to the reliving of past memories. There really isn't a mystery here; if the planet could get rid of Lavos by its will alone, it would, but remember that Lavos too has temporal powers of his own. The heroes of time are the best choice for dealing with the threat.
From: Common Questions