You'd probably need to kibosh them in say the 18th century for them to play second fiddle to Osterreich, or somehow have Austria pull a win over them in the Austro-Prussian War.
As for why they didn't try Anschluss earlier, it's because the other sick man of Europe, Austria-Hungary, was still quasi viable and not in the mood to be broken apart. They could possibly have done so if it collapsed, but there would be a bit of a hullabaloo over inviting more Catholics into Germany, which could've tilted politics in Zentrum's favor to at least some degree, them being a party for Catholics at this point in time.