Cold weather that makes dogs "lazy"

During the recent extremely hot tropical weather, the arrival of rain after a scorching day is always a  welcoming event. Especially if it happens at night, or one which lasts till the night. For me, I like things natural. If it is cold enough, I will not switch on the aircon/fan, but open up the bedroom windows, and relish the natural coolness.
Jon and Max seem to relish the cool period too. During a rainy period, they will be in their usual welcoming behaviour when I arrive home at night, but after their walks, they will not even look inside the house at me looking for attention. Instead they prefer to curl up and sleep. This will last till the next morning, when it is time to walk. Even then, I have to prod them to move on.
This morning was one example: Max - always preferring to be inside the cage when it is cold - slowly got up, put two front legs out, stretches the limbs, then out comes the hind legs. He stayed still while I put on the leash. I left him at his spot while I approach Jon. Jon was still curled up when I tied him. Now, both dogs are not moving. They are 5 meters apart. So I tugged Jon a few times for him to stand up. He got up reluctantly. I still needed to tug him to get him to walk. He does so reluctantly. Finally we got back to Max.
Once out of the house, they had no urgency to sniff and pee. I compare them to children, when they are woken up early in the morning to get ready to go for a car holiday trip. Despite the prospect of an exciting trip, with their state of drowsiness, they do things with all of their mind still on bed. Anyway, with the occasional sniffing and peeing, these two boys were mostly walking with their head at mid-level. They did not let out their first pant until after 500 meters.
Usually after reaching home on a cold morning, the boys will immediately settle down to rest. But today, Max acted differently. While Jon went off to rest, Max went right back in the cage with the leash still on him. He was already on his belly when I took off the leash.