After you miss a few memorials they get the message.
Just before the 2013 memorial I had three elders personally come to my house to deliver an invite. When I didn't show another elder came over a few days later to tell me my absence was an affrontment to Jehovah and the brothers.
We then discussed the memorial. I asked questions like:
If Christ told his disciples to do it until he returns, and he returned invisibly in 1914, why is the memorial still held?
Were there any "other sheep" attending the first memorial with Christ?
If Jesus instructed the 144,000 class to "keep doing this as a rememberance of me", why do the "other sheep" need to attend?
This went on for 30 minutes until he left.
Haven't heard from them since.