What does the severity of the average incident have to do with whether I use a particular mode of transit? We could add lots of fender-benders between taxiing

What does the severity of the average incident have to do with whether I use a particular mode of transit? We could add lots of fender-benders between taxiing planes to push down the average severity of each plane "crash." Then they would still be less deadly per mile travelled, but also less severe per incident on average than other modes of transit.