Mass invite guilds suck. That’s all they can do, because so little effort goes into them. People randomly show up and leave constantly because they aren’t actually looking for a guild, they’re just accepting a placeholder.
If someone has a reason to join a particular guild, that has staying power. There’s a criteria beyond merely reducing hearthstone cd or stopping further spam invites. A common goal or attitude. Even if they simply like the name, there’s some level of investment instead of easy come, easy go.