In leagues where managers typically struggle to attend every race, have an optional setting to limit the number of races that count towards the championship.
So for example in a 15 race league, if set at 80%, only a teams top 12 results would count towards the title race.withiut overly impacting their points haul
I'm really not a fan of dropped scores.
If people can't attend races either join a league that runs at a time they can attend or set up a league specifically for people who can't attend.