There were only a few Time-Tele-See-O-Matics left in time. Some were consigned to museums in the future. Others were lost to the bottom of tar-pits or deep in the earth's core. Most of the remainder were in the hands of artefact collectors, people searching desperately to find out what they were/are/will be.
But a few remained in the hands of skilled time travellers. These were men and women who could come and go in any era, causing only the tiniest of ripples in the space-time continuum. These few turned and guided the course of history. Trying to do what was best, they moulded the past into a better future.
As with any human endeavour, however, there were times when one or another of these people got it wrong. Or right, but at the wrong time, as the case may be.