Because you are seeing the current "template" of the infomercial.
they will insert phone number / web address as necessary depending on the day, week, channel, etc. that they are wanting to track....
if you made the phone number exactly the same....how could you tell if phone call was result of watching Biography Channel at 5:00pm, versus Discovery Health at 5:00pm same day?
Possible they could run ads on multiple channels at same time, having different phone numbers allows one to track it separately..which cable channel was lead in for call.
This allows them to examine a channel as well as effectiveness of certain times (better then others) etc.
All imo, I'm not the industry expert; but I do love tracking and analyzing data lol
I'm sure they will be gathering lots of data over next two weeks before escalating ads and channels. Don't want to be spending more $$ without probability those $$ are going to make you $$ or better yet $$$ or $$$$.
Market Data 
Markets 
AI
