Why TAU required even if in same TAC?

Hi Experts.
In LTE after RLF there is Reselection followed by TAU.
Can any help please help understanding the requirement of TAU even though if you are in same TAC?

Please check yellow highlighted part.

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As UE is lost …in order to have an update information about UE where about and whatever ID UE was assigned is released, so MME should get the new ID.

But UE is not detached.
It’s still connected with network.
It is in RRC idle state.

But think from network perspective that UE is lost.
To be on safe side developing such mechanism to avoid unnecessary paging to TACs and then globally.

3GPP does not define this.
It looks like a vendor specific implementation.
Otherwise even after RLF recovery MME would be able to page a UE.
Untill UE does not make any TAU update MME would keep track last TAC.

Could be and I will appreciate if anyone from the group answer us as most of the members from different countries and companies.

When There is a RLF,

there must be an indication by UE that RRC also disturbed to its NAS Applications, which in-turn pushes for a TAU as specified in 23.401.