Eh, I kind of get it. I've had my Deck ever since it came out and used the touchpads maybe two or three times in total. They are pretty pointless in my eyes.
First, that's your personal usecase. Second, they're very handy in some games were you have to select an area for example or when you're in desktop mode. I haven't used them that much either but they are useful.
I use both very often. Especially as a custom menu for emulator settings, or in older PC games or games with a lot of Keyboard/Mouse controls, they help me make things far more comfortable with various custom popup menus, or sometimes jumping to a mouse region to select UI options while playing. They are also helpful for games with horrid controls/hotkeys that won't fitnon a traditional amount of controller buttons. They also help with mouse precision when an analog stick won't do.
I also use the back buttons a lot. I use the entire Steam Deck and the custom controller settings are basically a necessity.