Because the development priorities right now are nowhere near PvP and it’ll take a long time for that to come by.
And considering the what the devs want to make GvG will be a priority to begin with and poeple openly want it, they already showed in the trialer a PvPvBoss in the trailer and everything iirc.
This kind of modes are easy to balance as they are designed as a showdown of the strenght of each guild, how they play togueter, how they built their characters and all that, this is the reason everyone loves WoE, it’s the ultimate testament to how good you are at the game and it’s made to be so
MOBAs ‘‘work’’ because due to the fact that you begin for 0 (or close) it’s easy to see when something is too strong and balance accordingly, which takes resources.
They are not meant as a showdown of sheer strenght, but of planing beforehand and doing so consistenly.
ToSs class design simply doesn’t allow for a proper enviroment for this kind of gameplay in general, comparing ToS to other MMOs out there is simply not a good option due to how diferent the system works and I’m sure IMC is aware of this, they are making a MOBA themselves and everything.