Response is marked as cacheable in \Magento\PageCache\Model\Layout\LayoutPlugin::afterGenerateXml only in case if there are no blocks in the layout of current page marked with cacheable="false" attribute, like this:

<block class="Magento\Checkout\Block\Registration" name="checkout.registration" template="registration.phtml" cacheable="false"/>

By default all CMS, product and category pages should be cacheable, their layouts were refactored so as not to contain non-cacheable blocks.

Also keep in mind, there is a bug related to usage of cacheable="false" on product pages described here.

Response is marked as cacheable in \Magento\PageCache\Model\Layout\LayoutPlugin::afterGenerateXml only in case if there are no blocks in the layout of current page marked with cacheable="false" attribute, like this:

<block class="Magento\Checkout\Block\Registration" name="checkout.registration" template="registration.phtml" cacheable="false"/>

By default all CMS, product and category pages should be cacheable, their layouts were refactored so as not to contain non-cacheable blocks.

Also keep in mind, there is a bug related to usage of cacheable="false" on product pages described here.