Sturm has taken on some pretty risky opposition.
Risky in that, most of the boxing world haven't heard of them, but they are quite good fighters. Meaning he could lose to them and end up looking like a worse loss than it was in actuality.

As for Abraham, I had high hopes for him, but he's dropped the level of competition since miranda.
It's possible that they got a fright in that fight, but saw it as proof enough of his quality, Allowing him to coast.