Titanoboa farmers - how long do your snakes last?

I play on a small family server. We've been eyeing taming a bigfoot, and to that end built a titanoboa farm like those on a few youtube videos out there. (besides, who doesn't want a snake pit?!)

The trouble is that the snakes are always gone when we come back. Now, I expected them to despawn over time - specifically, I figured if we spent a lot of time in other areas, the server would start killing them off to spawn new dinos in those new areas. I was expecting attrition based on how much we wandered and to replenish the snakes every few days if we were mostly local.

But that's not what I'm seeing. Leave the area for an hour? All the snakes are gone. Log off in the landing platform overlooking the snakes, then log in in the morning without anyone playing in between? All the snakes are gone.

In order to farm eggs, I have to gather the snakes and then sit around that area.

Is that what everyone else is experiencing, or am I doing something wrong?