Wood shrinks and expands with humidity, metal does not, most finishes barely change.
Metal shrinks and expands significantly with changes in temperature. Every change - multiple x per day. Especially the type metals often used in cues (stainless, silver). Wood barely does (separate from MC change).
Finish & glue is probably shrinking from conditions that cause metal to expand.
All 3 systems are fighting each other, sometimes multiple events per day, but it is mostly the wood and metal acting independently to slightly change size, all the time.
Some cuemakers and furniture makers have evolved methods to deal with it. Nonetheless, there are limits.
smt