When Magento 2.0 came out, the well-known feature from Magento 1 - to add the payment method as a condition for a cart price rule - was not implemented.
Magento 2.1 added this feature. Lately we updated a system to 2.1.9 and noticed that the feature was missing again. It is still present in version 2.1.7 and I assume it has been removed in version 2.1.8.
On Github, I think this is the commit that removed the feature: https://github.com/magento/magento2/commit/bb65d05d41f30cd6a10fdfffb10b1dd8f42d3a77#diff-6af1fa68376d90ae611de38779431624
Interesting enough, we have cart rules in place that were created with "payment method" as a condition and they are still working.
It would be nice if anyone could answer the question if I am missing something here, or if it's safe to write a small plugin for the function
loadAttributeOptions() and simply add the payment method again.