Clearly, your memory is failing you.
There were two delays for macOS X leopard, and Apple directly blamed iPhone development in their statement.
“iPhone contains the most sophisticated software ever shipped on a mobile device, and finishing it on time has not come without a price -- we had to borrow some key software engineering and QA resources from our Mac OS X team, and as a result we will not be able to release Leopard at our Worldwide Developers Conference in early June as planned.”
Apple has today announced that the release of MacOS X 10.5 Leopard will be delayed until October due to the development of iPhone. iPhone contains the most sophisticated software ever shipped on a mobile device, and finishing it on time has not come without a price -- we had to borrow some key...
www.macrumors.com
My speculation is also that the entire reason that “Snow Leopard” was ever a thing, was because iPhone software development had to move so quickly in those early days between versions 1.0 and iOS 4, that most of the people there who would have pushed for a big step right from Leopard to Lion were too busy Bringing cut copy and paste, multitasking and hundreds of other things to the iPhone.
iOS 4 was also delayed for the iPad, The iPhone got it on June 21, 2010, The iPad not until November 22.