It’s reasonably slow to go prone in ET. However, going out of prone is unreasonably fast. You get up from the ground carrying all that heavy gear in like one millisecond. Does this kind of encourage the use of prone more (which is more tiring) than the use of crouch? People nowadays go prone where they would have crouched back in RTCW original, unless you can’t see 'cuz you’re too low. This is great… but make prone a bit more unforgiving as one cannot stand up so fast from a lying down position.
Can anyone tell me why we can go out of prone so fast?
… your getting shot at, getting worked… ya hit prone and people(not u :P) think ya died, lmao…

Playability.
I think the developers realize that the game mechanics of dodging vastly outweigh the advantages of being prone. Prone is great if you can kill the guy at range quickly. If the enemy closes, you’re screwed. The guns are so accurate while crouched that I rarely go prone as it is.
The way the game plays today, prone people are already dead meat if you can sneak up on them.
So, since you can dodge bullets pretty effecitively (which is unrealistic) you can also jump out of prone fairly quickly (which is unrealistic).
When/if more realism is added to make sprint-strafing style fighting less effective, they can balance that with some realistic mods to going prone.