French autorities say that banning away fans for this match had little to do with the safety for Ajax fans but rather the safety for the Marseille fans. "Agressive behavior is something that is seen a lot with Ajax ultras, who mostly operate under the name 'F-Side'. They are known as one of the most dangerous groups of Europe."
In 2009 things already went wrong between the two clubs when Marseille and Ajax faced eachother in the UEFA cup. Ajax fans went with a big group of fans to Marseille. Ajax fans were then attacked by Marseille fans with bricks, sticks and iron bars. Ajax fans then chased Marseille fans until police showed up. In the return in Amsterdam Ajax fans held up a banner saying "We had joy we had fun, we had L'om on the run".
What Marseille fans did to Lyon's bus don't make a strong case for them, but it has mostly been French authorities taking the easy route.
Instead of deploying and organizing themselves to secure a safe environment for travelling fans, whoever they are, they just straight up ban them so it's easier for them, don't even need to bother.
And then when you have the UCL final, you have no clue how to manage fans.
Come to think about it, the French police aren't so different from my country (Indonesia). They're too lazy to think about solving the problems properly and they just ban things (and people).