>> So why wasn’t this a problem in 2008 or prior to that? >>
First, I would not assume it wasn’t “a problem” - just because it didn’t go nuclear. It could have been a bubbling problem for cycles.
Second, our world is changing. In 08, there was not the focus on debates and social networking and the internet there is now - so the old timey hand written signature thing was more of a focus for the campaigns.
Things change all the time, including how campaigns are waged and what rules become obsolete or meaningless.
Things change when you have candidates who are disorganized and poorly funded that they can’t comply with the rules.
It was not a problem in 2008.