It was explained that the Time War is time locked. In other words, anyone in the Time War is trapped, essentially in a separate universe, and this would incldue all other Time Lords.
The Master was outside the Time War, but was thrown into it in "The End of Time".
The Doctor can meet other incarnations of himself(but was unable to meet the War Doctor without outside help).
Remember also that most Time Lords never leave Gallifrey. The Doctor's renegade status was originally said to be because he wanted to get out and see the universe while most Time Lords were content to simply remain on Gallifrey"The War Games".