Why don't Time Lords from different Parallel Universes help out?

Question

In Doctor Who, the Tardis slipped into another universe. That other universe showed a different possibility of the "original" universe.

Q. Why didn't Time Lords from different universes enter the universes that lost the Time Lords?

Answer 1

I will assume you are referring to new Doctor Who, since the Time Lords were only lost in the gap between old and new.

In the new Doctor Who they maintain that parallel worlds are now (roughly) impossible to reach. That's why the Doctor is surprised to end up in one in episodes 5 and 6 of Season 2. With the parallel universes being sealed off, Time Lords from other universes cannot venture into ours in the same way the Doctor cannot venture into theirs.

The relevant quote from the Rise of the Cybermen:

Used to be easy. When the Time Lords kept their eye on everything, you could hop between realities, home in time for tea. Then they died, took it all with them. The walls of reality closed, the worlds were sealed. Everything became that bit less kind.

So the Time Lords being present allowed travel to parallel dimensions. Once they were no longer there, it "locked" the universe, preventing Time Lords from other universes from accessing ours and vice versa.

Answer 2

The first assumption you are making is that there ARE any other Time Lords from other universes/realities/timelines. There has never been a sign that there are other Time Lords from any universe other than the Gallifrey from our universe.

Theoretically, there should be other Time Lords from other temporal realities (assuming the theories of a multiverse or metaverse are potentially true) but no proof substantiates the existence of other Time Lords from other realities outside of our universe, and if there are, the Doctor has never made mention of them or their potential threat to the Multiverse at large. There are too many secrets the Gallifreyans kept to themselves about the true nature of the universe to know whether they knew of other temporal versions of themselves.

Perhaps a parallel universe Doctor has a differently colored TARDIS...

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I speculate the event that binds the Gallifreyans to their private little universe may have happened across every "near" continuity similar to our own, thus preventing any of them from reaching across to our universe easily. There are also many threats inside of the time vortex as well, threats from the beginning of the universe called the Chronovores which may have destroyed other parallel versions of the Gallifreyans.

Since the Gallifreyans were an insular race, they may have never established connections with their other inter-universal counterparts, assuming they existed. Indeed this may be doubtful, since the Gallifreyans chose to lock themselves away from OUR universe by establishing their own pocket reality where time moved at a completely different rate than our own.

The Doctor does mention there was once an ability to travel across the Void to other parallel universes but that ability was lost when the Great Time War locked the past all the way back to the Big Bang, preventing the Gallifreyans from escaping into the past and altering time so they could not travel to the far future either.

We have seen Cybermen from an alternate reality (the reality where Rose and the Doctor's one-hearted double are currently living) so we know there are multiple versions of certain things. But since the writers have prevented inter-universal travel, we shouldn't run into any OTHER renegade Time Lords from parallel universes.