1) I think some shadchanim are afraid to call pple back with neg. replies (once the shidduch already started), so they assume if they dont call back at all then the person will get the message.
2) I remeber a relative of mine had an older daughter and there was one shadchan that had very good ideas so she tried calling her numberous times and leaving multiple messages. After a while of doing this and being ignored, she called back but blocked her caller ID – of course the shadchan answered. When this woman explained who she was the shadchan said “the reason i didnt call u back is bec i didnt have whom to suggest for ur daughter. If I will think of something I will call u”.