The dog waiting at the door does not understand the reason you forgot the walk.

Your explanations do not travel across the species line. The meeting that overran, the day that broke apart, the genuinely good reason: none of it reaches the animal by the door, who only knows the thing did not happen. That is not an accusation of neglect, only a description of what an animal can hold. Their world is made of routine rather than context.

This is a design problem more than a guilt problem. Put the walk at a time your work cannot easily eat, or arrange someone who can take it when the day collapses. Ten minutes reliably is worth more to them than an hour occasionally.