First of all, at the moment when Hestia was born, I already had many servers with my own "quite a lot modified VestaCP" (at that moment fork didn't have a name).
So, it was not easy to port all those features (that I already had) to HestiaCP.
Simply, porting all those features would took too much time.
Plus, it would probably bring the bugs... and I didn't want to "play" with production servers of my clients... they are paying me for stable servers.
Secondly, to be honest, reason for staying with my fork is to have total control of code and builds, because I don't want to wake up one morning and realize that 120 servers of my company is down because something went wrong during auto-update of hosting panel.
I know how my servers are configured, and I'm careful with git commits (that goes later as myVesta updates).
When someone other is pushing new releases... well... everything can be expected... at least because he don't know if I'm using something specific on my servers.
So, it's subjective reason - specific to me and my company.
I'm not making myVesta to be competition to Vesta, I'm not making myVesta in order to get Vesta users and to have wide reach...
I'm making myVesta primarly for my own company... and because Serghey stopped to make official builds with fixes.
My fork is public just because friends asked me to share it with everyone.
I will maintain myVesta for sure, because I'm doing a business with it.
But if you need faster development and many new features - Hestia is better option because they have much more developers.
Of course, rapid development has it's own risks with code stability... but that brings us to the beginning of this post

Also, don't expect from me that I can be fast wtih making new features for myVesta.
I can't be fast.
I'm currently only one developer of myVesta, doing my primarly job in my own company, handling all my clients, and my day has only 24 hours.
myVesta will be developed with a speed that I can follow.