While pondering why this one negative gevura is mentioned in this berocha I came up with the following possibilities:
1. We throw in the ultimate negative gevura to show that Hashem is in charge of everything.
2. Some say that by ‘תחית המתים’ everybody will depart this life and then come back alive.
3. ‘ממית ומחיה’ could also be referring in a spiritual sense. Hashem constantly gives us extra closeness to Him and then takes it way to let us work on our own.
4. Since Hashem is the one that causes death, there is nothing stopping Him to resurrect the dead.
Please write in the comments additional explanations.