Especially for laptop CPUs. They’re usually tuned (underclocked) to use a tiny amount of power. Because power consumption and performance are non-linear, even old laptop CPUs are usually much more energy efficient than modern desktops.

You can underclock a lot of modern desktop CPUs to be more energy efficient too (eg Eco Mode). But almost nobody bothers to actually do that.

I recently did some minor testing of Eco Mode on my AMD build. I saw zero impact to single threaded workloads and a ~3% drop in performance for multithreaded. Which is a trade-off I will happily take.