When a lizard basks all day, it is because the lizards instinct is telling it to warm up and it's body is not able to acheive the temperature it is demanding. They don't read care instructions and their bodies know what to do. They've been doing it for thousands and thousands of years. Thermoregulation is just as important to their survival and just as instinctual as drinking and eating- they know what they need and how to do it. But just like we can mess up diet, we can mess up how we provide heat and do things that cause burns or cook our lizards, etc.
So that is the first thing to think about the other is age.
In nature, babies bask in the same sunlight as the adults- same temperatures. The only thing about babies is that they dehydrate and overheat more easily. So in a terrarium if they are in a poorly designed habitat without a true temperature gradient so they can escape the heat, or maintain the heat without being in the hottest part of the cage all the time. Also, chameleons do better forced to be a bit cooler than they desire than they do when forced to be a bit warmer than they desire. So for babies- it's a safety thing to recommend low basking temps. In general in fact- a little cooler is always safer than a little warmer, even for adults.
For adults- lower temps are recommended sometimes to lengthen the lifespan of veileds, especially females.
True temperature gradient- not a simple hot spot/on-off/ hot-cold situation. Lots of branches under the heat source so the lizard can choose lots of different temperatures at any given moment, as well as cool away from the light. If you do that, you can safely raise the temp a bit and your lizard will know what to do for itself and will not sit under the hottest spot all day, nor will it burn itself.
