Why are indexes not created on all columns and all combinations in a row?

Indexes speed up searches but create overhead:

• Take up additional disk space. The more indexes, the more memory and disk space are required.
• Slow down write operations (INSERT, UPDATE, DELETE). When data changes, all relevant indexes need to be updated, increasing execution time.
• Complicate query planning. An excessive number of indexes can confuse the query optimizer.

Therefore, indexes are created only on columns and combinations that are actually used in search conditions, sorting, or table joins, to balance read and write speeds.