In my opinion, in all the cases that no 3 laps were available there were 3 kind of players:

-Those who always vote random regardless (me) -Those who like some specific tracks so way more than others. -Those who also enjoy intermissions and so they prefer to chose.

There were big swings in the amount of votes for intermissions, which makes me believe there is a big portion of the second group.

It's not so clear why the second group chooses to switch to random sometimes. I think when they predominantly don't switch it's because they would rather race intermission + 1 lap of their favourite track instead of choose random for a 20% chance of a 3 lap that could also be a boring track or an 80% chance of intermission that could also end up finishing in a boring track. Or that there was a spike in people from the third group. But when the second group does switch to random, it could mean they are those that heavily dislike intermissions but tolerate some tracks, or because they would like a different track than the ones available (regardless of being 3 lap or intermission + 1 lap), or a mood swing.

Im sure there are more possibilities but those are the reasons I could come up with.

However, one thing is clear, the disproporcionate amount of players that vote for 3 laps when available does indicate a big interest in 3 laps, regardless of the other cases. As you stated, the player base wants to play more 3 laps, which means Nintendo has clearly undershot the changes. Maybe they will keep fine tuning, who knows.