A bin is a bucket of other people data
The moment you paste a bin URL into a payment provider, a CRM or an identity service, whatever that system sends starts arriving - and it does not send test data because you are testing. Webhook payloads carry email addresses, names, amounts, addresses, internal identifiers, and frequently a signing header that authenticates the request. All of it lands at a URL anyone who learns it can read.
Short retention is the response to that. The requests are there long enough to read while you are working and gone shortly after, so a bin URL that ends up pasted into a ticket or a chat channel stops being a window onto anything. A tool that keeps them for longer is more useful and more of a problem, and which of those matters more depends entirely on what you pointed at it.
Read the request rather than the documentation
The reason to use a bin at all is that integration documentation is frequently wrong, out of date, or describing a different API version. What actually arrives settles the argument: whether the body is JSON or form-encoded, whether the signature is in a header or a query parameter, what the content type really says, which fields are present when the documentation says they are optional.
That is why the raw body matters more than a parsed view of it. Pretty-printing a payload is convenient and hides exactly the things you are debugging - a trailing newline, a character set mismatch, a body that was double-encoded on the way out. Seeing the bytes as sent is the point.
What a fixed response costs you
Being plain about the gap: this bin answers every request the same way. If you need to see how your integration behaves when the endpoint returns a server error, or a redirect, or a deliberately malformed body, you need a tool that lets you set the response, and Webhook.site does.
Testing the happy path is the common case and a fixed response covers it. Testing the retry logic, the timeout handling and the error branches is the case where a fixed response is useless, and that is a real reason to use something else rather than a feature gap to apologise for.