creativepro.com - Adobe Talks: InDesign

"There are two things that Adobe said really helped the adoption of InDesign...the first was Mac OS X...Ironically, the second component that helped InDesign was Quark, according to Adobe. Quark was not as quick bringing QuarkXPress to Mac OS X, which left the market open to competitors..."

That's about it, Quark had pretty consistently been a laggard who offloaded new features onto third party extention developers. Mac OS X helped shine the spotlight on this tendency for sure.