The answer
Because they all close over the same variable i. Closures capture the variable, not the value. When the callbacks run, i is the final value, so all callbacks log it.
Closures Capture the Variable, Not the Value in JavaScript
Why do all setTimeout callbacks in a var loop log the same value in JavaScript?
More FAQs in Closures Capture the Variable, Not the Value in JavaScript
The variable. A closure holds a reference to the variable, not a snapshot of its value. If the variable changes before the callback runs, the closure sees the updated value. This is why var in a loop logs the final value.
Use let (creates a fresh binding per iteration), or an IIFE that passes the current value as a parameter (pass-by-value for primitives), or pass the value as an extra argument to setTimeout.
It captures a new parameter (j), which is a copy of the value (for primitives). The closure inside the IIFE closes over j, not the outer i. So even if i changes later, j holds the value at the time of the IIFE call.
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