Probably because it's easier for parliament to point fingers at a bank and convenienly ignore it's own inefficiencies.
"Unfortunately this online service is currently unavailable.
We’re very sorry for any inconvenience. As soon as we’re able to, we’ll update this message to confirm when the service will be available again.
If you need to meet a payment deadline or have an urgent tax query that needs addressing today please go to gov.uk/contact-hmrc for details of how to get in touch.
You can use the alternate contact methods on HMRC contact pages to ask a question, report a problem or suggest an improvement."
