Slides came about because these games want to have “realistic” ADS-style gunplay, which is pretty incompatible with movement. Sprinting, jumping, climbing, pretty much doing anything gives huge accuracy penalties to your gun, and ADS literally slows you down so you can shoot straight. The solution they came up with was sliding so that you can actually move fast AND shoot straight for a short period of time
TF2 and other quake-style games avoid this problem entirely by just letting you truly run and gun