In short.
Combining the analyses of Professor Elm, Professor Rowan, and Pokémon Professors from many other regions.
The reason the Dragapult line formed a relationship similar to "symbiosis" with Dreepy during the Drakloak stage.
Was largely because they were far too weak during their time as Dreepy.
According to information provided by the Dragon Tamer Family of Blackthorn City.
Not only did Drakloak carefully look after Dreepy, but once a "symbiotic" Drakloak suffered defeat in battle or showed itself to be inadequate.
The latter would immediately leave without a word.
This highly unusual phenomenon left many Pokémon Professors marveling in amazement.
It might also have a lot to do with the fact that they were not parent and child.
At the very least, similar cases, such as Kangaskhan, did not display this behavior.
In Professor Oak's view.
"Rather than calling the relationship between Drakloak and Dreepy 'symbiosis,' it would be more accurate to say they are making use of each other."
That was what he had said at the time.
"Dreepy needs a stronger Drakloak to protect it, while Drakloak also needs to obtain a way to become stronger from Dreepy."
This speculation did fit the habits of ordinary Pokémon.
The only puzzling question was how Drakloak became stronger.
"Willpower."
It was Professor Rowan, who studied Pokémon evolution, who gave the answer after conducting extensive data analysis.
"Unlike ordinary Pokémon, the Dragapult line seems to place great importance on the strength of one's will."
Among the energy data charts for several Dragapult provided by the Dragon Tamer Family.
There was one piece of data that stood out in particular.
It was "Body Transparency."
To be honest.
When Tetsuya first saw that entry, he had been thoroughly baffled.
After all, he had never seen any other Pokémon with a similar statistic.