There are several users who would be receiving the watchOS 6 beta by invitation from Apple itself directly to email. In this case, what Apple is trying to do is to improve the version of its OS for the Apple Watch with more tests and users, so in this case it is sending invitations to test watchOS 6 to several users.
By means of an email, participation for the beta is invited and the user is always the last to choose whether or not to install it on their smart watch. Logically that Apple invites us means that the version is working stably, although it will have its small flaws but it is stable.
It seems that not all developers would be installing this beta version of watchOS or is that Apple really needs more "feedback" than it receives from all developers, so they open the AppleSeed, which is the program to invite users to test the latest beta version of the OS on your Apple Watch released.
As always in these cases, the first thing we have to say is that the invitations have to arrive in the mail from Apple and there is nothing you can do or try to get this invitation sent to you, the decision always depends on the brand itself. In addition, it must be clear that getting into these beta versions for the Apple Watch is not like doing it on an iPhone or Mac, that we can always go back in case of problems, on the Apple Watch installing a beta version means not being able to go back and return to install watchOS 5, so this may cause some other compatibility problem despite the fact that, as we said at the beginning, the watchOS beta seems to work quite well and that is why Apple randomly invites users for a chance to try it.