They, the mega whales, want to keep dominating the markets and not let today's bitcoin owners become more powerful and wealthy than the mega whales. And those big traders can easily launch their own cryptocurrency once legal regulations are in place.
Hey! I came to think of another possibility. Governments will not allow any independent cryptocurrency to become too big. They will therefore introduce an official cryptocurrency.
Easier said than done. How do you propose they not allow bitcoin to become too big? And why would anyone else use their cryptocurrency?
The total value of bitcoin today is puny compared to the trillions of dollars being swapped around on the fiat exchanges. If some of the really big players decide to cooperate and issue their own cryptocurrency they can easily and quickly pump up the price of that currency, and then the smaller investors would start to follow in order to gain on the massive upward momentum. In this way their cryptocurrency could match bitcoin within a couple of months and then go up much further leaving bitcoin behind like pocket change.
OK, so they spend a bunch of money to create a currency that they control. Then they put it up on an exchange, that they also control, and as people trade it, start buying MASSIVE amounts for billions of dollars, to pump up the price to Bitcoins level. But, all they really did is create another PalPal, with a floating exchange rate, while having none of the benefits offered by Bitcoin, since their currency is not decentralized, not anonymous, not politically neutral, is entirely backed by their company (as opposed to not depending on engine), and completely closed off to development and innovation. As soon as they stop dumbing billions of their own dollars to pump it, that currency will crash back down to almost nothing, as people exit back to the only currency that actually has the features they were looking for in the first place.
This whole exercise would be as if Microsoft were to make their own Linux, pump it by PAYING you touy it, but leave everything that makes Linux competitive out of Linux (bad security, closed source, etc.).