TLDR: it’s random
Ever sit patiently for days and days and wonder why a certain Animal Crossing: New Horizons guest never shows up? Well, someone got to the bottom of it.
The ever-reliable New Horizons dataminer Ninji took the case and came back with some surprising results. As it turns out, you’re guaranteed to get Leif (gardening), Kicks (footwear), or Saharah (rugs) on weekdays (with the requirement of the Able Sisters for Kicks and a house for Saharah), which is why you probably see them so often. The issue, however, is with Flick (bugs), CJ (fishing), Label (fashion), Gulliver (washed up on shore quest), and most notably: Redd (art).
Here’s the catch. Although the former trio is guaranteed to show up, the latter five cycle in randomly to fill those errant weekday slots. In other words, you may not see any of them for quite a while, in spite of the “bad luck prevention” measures New Horizons has installed.
Yep, just like some loot box mechanics, if you “miss out” on one of those in the latter category, you’ll have a higher chance to see them. But note the phrase “chance” here, as there’s no guarantee, and you could go several weeks without meeting one of those critters even if you play every single day.
Reggie is right: this game is stingy! Multiple guests wouldn’t break the game, Nintendo.