Small is easy to maneuver but vulnerable. Spends time avoiding getting run over, and taking small bites to grow.
Get bigger, you move slower but can swallow bigger prizes. Unfortunately you need bigger prizes just to maintain your current size while continuing to avoid even bigger players.
Get really big and you don't have many predators. You can't really move all that fast anyway, but it doesn't matter because everyone is avoiding you. And because you're just coasting you can maintain your size for a really long time.
And at all sizes, you much prefer swallowing something you know you can handle, rather than go for the big prize that just might be too big.
Get bigger, you move slower but can swallow bigger prizes. Unfortunately you need bigger prizes just to maintain your current size while continuing to avoid even bigger players.
Get really big and you don't have many predators. You can't really move all that fast anyway, but it doesn't matter because everyone is avoiding you. And because you're just coasting you can maintain your size for a really long time.
And at all sizes, you much prefer swallowing something you know you can handle, rather than go for the big prize that just might be too big.