Take The Bet

In practice, there’s a finite number of encounters used to start typical new campaigns. There’s no shortage of low level/ challenge monsters, but many are just used in mobs at higher levels or as secondary encounters. The first encounter tends to be more iconic. A big name critter. You’re likely to fight kobolds over monodrones and goblins over grimlocks. 

There’s lots of reasons for the first encounter to be “boring”. It might be because the group is trying a new edition of variant of the game and wants to start with a familiar monster. Or they’re returning to low levels after a stint of high level play and are taking the opportunity to bring back a favourite monster unseen for many, may levels. Or the group might be new and the opportunity is being presented to introduce the players to a classic D&D monster.