system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who The Big Bang] How did a single Tardis exploding cause the destruction of the entire universe? Not forgetting hundreds of Tardises were being destroyed every hour in the Time War yet the universe carried on just fine.
gpt
The Type 40 Mk III TT capsule was long out of service before the Time War started, and with good reason: its Heart does not include the fail-safe implosion mechanism that other TT capsules were required to have in order to *prevent* timeline destruction.

When (for example) a Type 56 is destroyed, it makes a supernova-scale bang and some mild local spatial events, but that's about it. When a Type 40 goes up, *everything else goes up with it*.

The only reason that the Type 40 stayed in service for so long was that, back then, the Time Lords had no enemies capable of destroying a TT capsule. Even then, a number of close-calls convinced the Time Lords that something had to be done about the Type 40's fail-deadly Heart. This prompted a partial redesign resulting in the short-lived Mk IV iteration (famously used by the Monk) that included an early automatic imploder among other new features, but the Type 40 family as a whole was rapidly superseded by newer, safer, and more capable models that included the implosion system by default.

**TL;DR** The Doctor's TARDIS lacks a safety feature that all the in-service TARDISes have.