Why is Meetup.com not blocking spam in Meetup Groups?

I am member of dozen meetups everyday I get about 10-30 spam messages that are posted to the various meetup groups. Social Media is full of complaints, but there is nothing happening. Since months Meetup didn't provide any statement or announced actions they are taking. Although, the messages are pretty much following the same pattern why isn't it possible to block such messages automatically with common spam filters?