If all Timelords can travel back and forth through time, despite being wiped out of civilization, shouldn't the doctor and gang have bumped into one or two at this point? Pre Time War Timelords traveling pre Time War.
And IF they have been wiped out of time and space, why then are they remembered?
Apart from the Master in the classic series there was the Meddling Monk who the first Doctor met a couple of times on Earth, the fourth Doctor met Drax, the sixth and seventh Doctors met the Rani.
Gallifrey is/was an isolationist society, and external time travel is culturally taboo.
The celestial intervention agency only intervenes in events that might have hugely catastrophic consequences, and usually manipulate the few rogue timelords (who do travel, violating taboo) into doing their dirty work for them.
As @Lighthart noted, not that many Time Lords left Gallifrey as a matter of course to begin with, so there wouldn't be that many of them swanning about anyway. And with the whole of spacetime to romp around in, that's a lot of wherewhens to contend with, so the chances of running into another Time Lord purely by chance would be extremely slim.
But more central to that, I think, is that Gallifrey tends to be internally consistent, time-wise. That is to say that the "clock in San Dimas is always running," as it were. It's impossible, for instance, for the Doctor to go back to Gallifrey at a point in time before the Time War, for instance, because it's crossing his own timeline. (Yes, I know, it happens in Listen. But that wasn't the Doctor, and Clara is -- sigh -- the Impossible Girl.)
This would keep Time Lords from meeting each other out of order, except under very exceptional circumstances. The possibility of paradox becomes too great otherwise. Imagine if the Eleventh Doctor he were to meet, say, the Third Romana, and warn her about the Time War. That could radically alter what would, presumably, be a fixed point. And we've seen what can come with mucking about with fixed points. (There's an Eighth Doctor novel where he receives a distress call from Susan and, rather than responding, tries to track it back temporally to rescue her before she sends the call. He encounters the Master at an earlier point in his timeline and winds up creating the very circumstances he was trying to prevent -- effect precedes cause.)
So, since all the Time Lords are moving forward in time at the same rate relative to Gallifrey (or, possibly, relative to the Eye of Harmony, if I may speculate a little), then no matter where the Doctor goes, the Laws of Time will prevent him from landing in a wherewhen that would bring him into contact with an earlier version of a Time Lord.
Gallyfrey is in the Time War, in a Time Lock. It means that it has a past, because it has existed, but it is excluded from normal time.They substract thenselves from Time and Space, into another dimension?, world?, space? I don't know... But the point is that they only stay as a legend , like when the Doctor was ereased form time and Space, he stay as a story in Amy's head. Also I think that Gallifrey must have some kind of protection against Time Travelers, to prevent travelling from another Time Zone, or from Gallifrey's future.
Another important point is that the Doctor have bumped with 1 or 2, like the Monk, but the Doctor is a exilled Time Lord from Gallifrey because of something that he have done. It kind of explains why the Doctor try to avoid other Time-Lords. EDIT: This is the Classic Doctor Who, in the actual he is the opposite.
It is forbiden to meddle the doctor breaks that rule a lot it is possible they had constantly but were unaware because they were just another face in the crowed, but when the time war startend one can asdume it was like a draft and all timelords werecalled in sealing their tmelines in the quantam lock the doctor being of the race that can precieve all events in time he can remember them like when rory was erased from time
