Thing is, we don't know that. We only know what happened AFTER Amber moved in. There is a video that Amber posted, soon after moving in, where she's jumpy and looking around and at some point she mentions Eric came by/walked by (she was eating something in the den).
It lead me to think Eric was already a stay-at-home husband by the time Amber entered the equation.
The underwear photo on FB was posted years before Becky met Amber.
Amber might have been the catalyst, but the traits were already there. No one in their late 20's with responsibility, work ethics and common sense would just give it all up because the over-grown baby moved in with them.
Becky and Eric were always this nasty and lazy, we didn't know it because we didn't see it. Amber just brought our attention to them, and they are happy enough to show their asses on social media.
I reserve judgement on Ricky, but at least he's smart enough to keep his private life private (as much as he can. What with his husband shoving a camera on his face whenever he can).