This is because there are two notions of “identity” in regards to the Subspace Network. There is the Farming Identity & the Reward Identity
Farming Identity: This is the identity assigned to each unique farmer, and the identity that actually signs the block, and is “punished” in the case of acting badly on the network. Since plots are associated to the farming identity, if your identity is slashed you are forced to re-plot.
Reward Identity: This is your Wallet Address, the one where rewards will be sent, and the one you should really care about.