Almost always one of three things: the operator's manual approval queue has not reached your request yet, your identity verification is incomplete, or the amount triggered a second anti-money-laundering review.
The three real causes
The approval queue. Most operators approve withdrawals in batches worked by a payments team, sometimes twice a day, sometimes once. Until your request is picked out of that queue, nothing happens. This is the most common cause and the least visible, because the account just says pending.
Incomplete verification. If you have not completed know-your-customer checks, your first withdrawal triggers them. Everything stops until documents are reviewed. The account may not say this clearly, so check your email and the document upload section of your account.
A second review on the amount. Larger or unusual withdrawals get a second look from the anti-money-laundering team. This is a licence condition, not an operator being difficult.
How to tell which one you are in
Open your account's verification section. If anything is marked outstanding, that is your answer, and uploading the document is the only thing that moves it. If verification is complete and the amount is ordinary, you are in the queue and waiting is genuinely the answer.
Live chat can tell you which of the three applies. Ask specifically: "is my account fully verified, and has my withdrawal been approved yet?" That question gets a useful answer where "where is my money" often does not.
What does not help
Cancelling and re-requesting the withdrawal puts you at the back of the queue. Some operators deliberately make cancellation easy because a cancelled withdrawal often ends up being gambled instead. If you see a prominent cancel button next to a pending withdrawal, that is what it is for.
When to escalate
If verification is complete, the amount is ordinary and it has been more than three business days with no explanation, raise a formal complaint with the operator. If that fails, escalate to the regulator that issued its licence. UKGC, Spelinspektionen, Spillemyndigheden and the KSA all take payment complaints seriously, and an operator that ignores its regulator has a much bigger problem than your withdrawal.