The time period "all" was removed from version 4.0 and the functionality was changed to zoom to 2 years by default in 3.4.14.

This feature request was made to discuss possible solutions to bring back such a feature.

It seems, that with the slider bar gone, the problem with heavy SQL query is also gone (ZBX-12066), so making the period "all" look for the oldest record and zooming to "all available data" would bring it back.

But this would not happen by default, only by the user explicitly clicking on the link.