Pokemon as a franchise has been going strong for the past 26 years, and while every new addition to the mainline series comes with multiple new features to make the gameplay loop more interesting, there are several traditions that have been kept in place for the longest time. Even though Gen 9 games are already revolutionary due to the fully open-world setting, Pokemon Scarlet and Violet broke long-standing traditions in terms of tall grass and line-of-sight trainer battles, which had been a staple of the series ever since Gen 1. This is not necessarily a bad thing due to innovation often requiring bold changes that take away even some of the most deeply-rooted elements of a video game franchise, and Pokemon is no exception.
A great example of innovation came from Gen 7's regional forms, which allowed Game Freak to revisit fan-favorite Pokemon from past games and tweak their designs in unique ways enough to make them almost entirely new species. On the other hand, an example of a lack of innovation is that Pokemon games almost never strayed from making pseudo-Legendary and Legendary Pokemon anything but Dragon-type. This is something that Game Freak pigeonholed itself into for a number of reasons, and unfortunately, Pokemon Scarlet and Violet don't break this tradition but confirm it once more.
A History of Pseudo-Legendary and Legendary Pokemon in Mainline Games
Dragon-type Pokemon were not always a key ingredient of Pokemon games, to the point that Gen 1 only had three in the form of the Dragonite evolution line, and Gen 2 even had just one in the form of Kingdra, shockingly enough. However, this didn't hold true from Gen 3 onward, as Pokemon Ruby and Sapphire introduced a Dragon-type pseudo-Legendary with Salamence, as well as Dragon-type Legendaries with Latios, Latias, and Rayquaza. Gen 4 did something similar, with Garchomp as a pseudo-Legendary and the creation trio all being Dragon-type Pokemon and being each game's box Legendary, including Pokemon Platinum.
Gen 5 had a similar pattern, with Hydreigon as a pseudo-Legendary and the box Legendaries being Reshiram and Zekrom, first, with Kyurem added into the mix. Gen 6 featured Zygarde as a Dragon-type as well as Goodra as a pseudo-Legendary, even though Pokemon Sun and Moon didn't have any Dragon-type Legendaries apart from Kommo-o, the generation's pseudo-Legendary. Pokemon Sword and Shield included several Dragon-types with Dragapult as Gen 8's pseudo-Legendary and both Eternatus and Regidrago as Legendaries. Pokemon Scarlet and Violet didn't break the mold either, and they feature Baxcalibur as the games' pseudo-Legendary, while both Koraidon and Miraidon are Dragon-type critters.
Why Dragon-Type Pokemon are More Likely to be Legendary and Pseudo-Legendary
The reason why Game Freak seemingly can't break away from this pattern is that it made Dragon-type Pokemon both rare and relevant in terms of lore and gameplay too, which means that making new Dragon-types is a process that needs to be balanced carefully. This is probably the reason why there are no Dragon-type Pokemon early in the game, and most of the new ones end up being ones that players can obtain later in the region, which carried over even in Pokemon Scarlet and Violet despite the open-world setting.
As such, it's only fair to assume that future games in the mainline series will struggle to add new Dragon-type Pokemon that are not Legendaries and pseudo-Legendaries, as those are the easiest to label as both rare and powerful regardless. For example, while Pokemon Scarlet and Violet's type combinations are great because they add many new ones, a Bug/Dragon hybrid wasn't introduced, and it's going to be a difficult one even in the future. Bug-type Pokemon are commonly found early in the game, and they don't tend to be among the best in any generation, but this concept contrasts the way Game Freak designs Dragon-types, instead, meaning that players shouldn't hold their breath for this type combo to come anytime soon.