Why does the Add to Cart button not show for some products for the United Kingdom?

Why does the Add to Cart button not show for some products for the United Kingdom?

SMART Recovery USA has a license agreement with UK SMART Recovery so we are not able to sell some of our publications to the United Kingdom. Specifically: the SMART Recovery Handbook, the SMART Recovery Facilitator Manual, and the SMART Recovery Family & Friends Facilitator Manual.

You can order the UK SMART Recovery Handbook through the UK site here: http://www.smartrecovery.org.uk/resources/bookshop

For the UK Facilitator Manuals, contact the UK SMART Recovery central office here: http://www.smartrecovery.org.uk/contact/office/