Do you really think the ability to reset your account completely back to zero, or start a new account, will turn RR2 from bad into number one game of the world?
Well, many high lvl and top lvl players already HAVE several accounts, so absolutely no need for changing the game for achieving that.
Also, when one spends money and a year of time or more just to reach the top lvl gameplay, why would they then like a feature to reset all of their hard-earned progress for which they have spent so much time, effort and money? Let me make this clear: Most high lvl players have at some point spent gems, and many have also spent money for buying more gems, in order to speed up their progress and get this or that upgrade done earlier. Why would they now perform actions to reverse all their progress again?
Moreover, the amount of lvl 120 players is VERY small - I still only know one account that has reached lvl 120, and that was achieved using a massive amount of gems for speeding up the lvl-up progress. With 99.999% of all players not being anywhere near reaching lvl 120, this definitely is not an issue.
Most important, reaching king lvl 120 is the very very last thing you will ever do in this game, and long before you will be done with everything else. So if you get bored due to a lack of new content or variety, you get bored way before you even get close to lvl 120.
And, last but not least, yes, recently many players have quit, and many more think about quitting, though I know not a single one quitting due to the lvl 120 limit. Players quit because there are issues with the game, at a stage where they already are, that makes the game not appealing to continue anymore, so players quit because they don’t like the game in its current shape anymore, not because there wouldn’t be anything new or different at all to unlock anymore.