Maybe announcements could be made more selective for different ratings ranges. That would help.
The main problem with announcements is, that they're only visible for those members, who're using Chess.com with a browser.
On the other hand, the only way to bring someone, who is using the App to a match ... is sending a personal message with an active link.
Chess.com's demotivating attitude towards clubs, their admins and leagues lasts (without any element of improvement, benevolence oder even understanding) already for years.
@tricky_dicky is completely right, but most likely Chess.com's attitude isn't some kind of an unintended problem in details, it looks to be an intended decision to limit admins and their interactions with members.
The intention is that if you need to message a lot of members is to use the Announcement feature. That allows members that don't want to receive club communications to opt-out.