what does Linux have that I need?

• Better interface than Windows (KDE WM)
• Stable and noo downtime internet speed like Windows because background update, can increase your internet speed to 40% (can up to 80% in my case with Q4OS + pure profile installation)
• Customizable interface according to your preference (with learning curve first)
• As a home desktop, there's so many useful apps from Linux (Recoll for example) that you can't find on Windows
• Very lightweight and power save (according with the linux you use)

What can motivate me to migrate?

IMO when you migrate to Linux, you can learn many things that you never think about before and it give you the easiest solution for daily life. From piracy, privacy, ideology, and deep tinkering other things that you can't do on Windows (Coreboot / Libreboot, or HAM Radio hack for example).

What is a good Linux to have for a desktop + steam?

Pop! OS is the best choice you have. But if you want to create home desktop for your family using it, I recommended Q4OS with Pure Profile installation, just install Firefox + Ublock Origin and you can go perfectly good..