There are 2^128 ipv6 addresses.

If you store 1 bit (banned/unbanned) + a unix timestamp (ban expiration) for each of those IPs, that requires more storage space than exists many billion times over.

To store such a block table you propose would require more memory for routers than any router has ever had and ever will have.

An attacker could easily "flush" all entries in this table by, for example, banning a TB of ipv6 addresses from talking to them, surely resulting in all participating routers dropping other bans to store some of those.