It could even be that Zero was introduced as an alternative for Zcash, if Zcash does not bring the success that at least Zero successfully starts.
Since this is not the case, it can be that the developer has even invested money in Zcash and thus it makes little sense to promote Zero further.
I personally think about boycotting Zero, maybe you hear something from the developer
Seems strange, betting against his/her/their own project. And also this coin launched well after Zcash, so I don't think this is the case at all.