Who uses a desktop? Are you trying to flaunt your ignorance?
Maybe you've never done video editing?
Right now I'm using a Surface Book Pro - a great machine for travel, surfing the internet, email and such. But it's a terrible machine for video editing, especially 4K (you do know what that is?
). My desktop, OTOH, I designed for video and photo editing - fast PCIe 4.0 SSD, humongous media storage drive, fast video card picked for video rendering, dual photo monitors etc.
But I knew what I needed. The same thing applies to DIY ebikes - if you know what you need, and know what you're doing, by all means build your own. But I didn't, so I bought a Trek, and a year later, I'd do the same.