The reason is that *Cluster are not a table engines, but a table functions. Using those tables can lead to logical errors:

CREATE TABLE test AS s3Cluster('test_shard_localhost', 'http://localhost:11111/test/a.tsv', 'TSV', 'a Int32, b Int32, c Int32')

SELECT *
FROM test

2024.12.24 14:48:19.456375 [ 757192 ] {0383f3dd-f998-4662-86ca-d3346e1ab872} <Fatal> : Logical error: 'Expected SELECT query from table function S3, got 'SELECT __table1.a AS a, __table1.b AS b, __table1.c AS c FROM default.test AS __table1'

Changelog category (leave one):

• Not for changelog (changelog entry is not required)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

...

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

CI Settings (Only check the boxes if you know what you are doing)

All builds in Builds_1 and Builds_2 stages are always mandatory
and will run independently of the checks below:

• Allow: All Required Checks
• Allow: Stateless tests
• Allow: Stateful tests
• Allow: Integration Tests
• Allow: Performance tests
• Allow: All Builds
• Allow: batch 1, 2 for multi-batch jobs
• Allow: batch 3, 4, 5, 6 for multi-batch jobs

• Exclude: Style check
• Exclude: Fast test
• Exclude: All with ASAN
• Exclude: All with TSAN, MSAN, UBSAN, Coverage
• Exclude: All with aarch64
• Exclude: All with release
• Exclude: All with debug

• Run only fuzzers related jobs (libFuzzer fuzzers, AST fuzzers, etc.)
• Exclude: AST fuzzers

• Do not test
• Woolen Wolfdog
• Upload binaries for special builds
• Disable merge-commit
• Disable CI cache