I prefer "Durable, but as light as possible", not the other way around. Most ultralight gear breaks after a few uses or when it is mishandled in anything-less-than-perfect conditions, which, happens a lot outside.
The pads do list their insulation value, but so do non-ultralight sleeping pads.
The reason is that the insulation value is incredibly important to comfort. From experience, a sleeping mat that is thick, but with bad insulation will lead to a way less comfortable night than a thin one with good insulation.
Sleeping bags don't provide much insulation on the bottom because they are compressed under your body (the insulation from a sleeping bag typically comes from air trapped in the fill). Any insulation between you and the cold ground has to come from the sleeping mat. That's why it is important to get one that is cushioned enough for your body as well as being insulated enough.
R values aren't an ultralight camper thing, they are an informed camper thing.
Very different philosophy behind this kit (durability and flexibility), but here's a good intro.
https://www.youtube.com/watch?v=Kin_bjAYk0Q
EDIT: I forgot he also has a more "ultralight" full backpack kit:
They're just marketed by R-value because better insulation will cost more. Many people don't camp in places that would require a high one.
But unlike India British Columbia is a completely different climate. We can go from very comfortable sunny warm days to very cold nights. The last time I went camping it was May and the days were nice but the night dropped down to like 5c. I have teens and told them all to pack lots of warm clothes, told them it will be cold at night, made them bring extra blankets. But in the end they still did not have enough and in the middle of the night were so cold. So I gave them 2 of my blankets and some of my clothing. This left me absolutely freezing. I had to finally get up at 1am and make a fire. I struggled to warm up and even had to go start my car and put on the heat for a bit. I put a large rock on the fire and got it hot. I put the rock into a cast iron pan I brought and put it onto a couple sticks in my tent so it would not burn the floor. I had to keep that rock close to me all night and I still was cold and miserable.
So yes on a warm night, and we have those here in BC, a pad is not essential at all. But for the other 10 months of the year if you don't have the right gear you will be cold and miserable. Being directly on the ground is like sleeping on a cold water bed (yes I am that old). It feels refreshing at first but then you fall asleep and wake up with your core temperature stolen and cold.
A solid pad in Ultralight often also doubles in the backpack as a replacement for what would be the frame in traditional backpacks, so it's dual use (or triple, if you consider using it as a sitting mat when taking breaks.
Also, sleeping bags typically compress under your body and lose isolation because of that, so with a pad you can use quilt-style sleeping bags (they wrap around the top and sides but not bottom, which makes them again lighter).
I was a restless sleeper though and had/have extreme difficulty getting to sleep often; learning to sleep on my back helps. Expressed another way, if my brain says I have to be on my side for comfort, and I have to achieve comfort to sleep, then if that comfort isn't achieved no sleep for me. Getting my brain to accept "and now we lie down for sleep" without thinking about comfort let me be actually comfortable in more positions/settings.