Why walking meditation is not mentioned in the ways of attending to mindfulness?

Namo Buddhaya. Buddha talks about walking meditation at several places in the suttas for example [here](https://suttacentral.net/an5.29/en/sujato) . However he doesn't mention it in the Long discourse about the ways of attending to mindfulness . There are 4 ways of attending to mindfulness but none of them mention walking or walking meditation. My questions are : Why doesn't Buddha mention about the walking or walking meditation in the long discourse about the ways of attending to mindfulness? Is there any sutta where Buddha talks about the technique of walking meditation?