They've discovered long enlightening dialogues are not cost effective in time usage to sales made. Therefore they've established a rationalist blacklist who they avoid calling.

Why do I never have discussions like this with telemarketers?

Have you ever tried? As it turns out, I haven't. On the other hand, when I was a kid, I remember my dad once giving an entire sales lecture to a telemarketer (he was a sales manager at the time) who was demonstrating poor marketing skills.