It’s interesting to look for patterns there.

• Most monotypes are well represented (10+ mons of that type). Flying is an exception.
• Pure Normal and pure Water are extremely common (80+). I think that they’re mostly land and sea route fillers?
• Types that you see combined with all other types: Dark, Electric, Fighting, Flying, Grass, Psychic, Water.
• If I counted it right there are 10 combos missing. Four of them involve Normal with Bug, Ice, Rock, Steel; the other six are Bug/Dragon, Ghost/Rock, Fairy/Ground, Fairy/Fire, Fire/Ice, Ice/Poison.

Dual types that are specially well represented (10+):

• Flying/Bug, Flying/Normal - mostly as land route and forest fillers. The abundance of Flying/Normal is almost certainly related to the scarcity of pure Flying mons.
• Poison/Grass, Poison/Bug - notice how a lot of them are from Gen 1/2, specially Gen 1. Kanto has a lot of Poison types, and that was actually a balance problem back then because Psychic was overpowered…
• Water/Rock - they’re a bit more well spread across gens, but note how four of them are resurrected from fossils.
• Fairy/Psychic - mostly from retconning older pure Psychic types into Fairy/Psychic, as Fairy was introduced as a type.
• Grass/Normal - artefact from how they’re counting different forms as their own species; eight of the 11 are a single evo line (Deerling and Sawbuck) in their four seasonal forms.