I still build my own PC(s) and never buy one prebuild. However technology now moves pretty slowly so I rarely really need to do it. The most you end up changing is just maybe a RAM upgrade and graphics card.

My PC lasted me pretty much 6 years with only a graphics card and RAM upgrade along the way - It was still able to play all games at Max and the only real reason why I recently build a new PC, is because I wanted a smaller form factor for living room play.

It's certainly not like the mid 90s or pre-2010 when technology moved so fast that you needed to upgrade at least every couple of years.