How do these exist in 2015?  It’s like wtf, how hasn't the internet made these irrelevant yet?  The last time I remember redeeming one was 7 or 8 years ago from a retail store, but now I'm going to be building a pc and half the parts I'm ordering online have mail-in rebates.  Do they only exist to be a pain in the ass, and therefore cause many consumers to not redeem them?  

I remember my first and only time sending in one of those. It was for a USB drive I bought like 10 years ago. $25 with a $10 rebate. I was so pleased with myself after sending it in...only to get a letter back saying they didn't receive the bar code that I definitely mailed to them.

Never again.

It does seem so archaic now...though I suppose it's easier to get around paying rebates if there's no electronic confirmation, so maybe they make more money this way. Idk...I suppose I'm just jaded.

Or it was mailed in 'late'.  I remember one having a ridiculously short return period and actually missing out on it.

I bought a $200 phone with a hundred dollar mail in rebate a while back. Didn't plan on spending any money but the rebate sounded good. I got home and didn't have the receipt for the rebate. The Verizon store never gave me one. It was all done digitally!

So yeah, it's to get you to forget about it or procrastinate or whatever little loophole stops you from collecting.

Less than 50% of mail in rebates actually get redeemed. Good for marketing, although I avoid anything with a mail in rebate, assuming it's probably a scam.
I used a mail in rebate once, did everything right, cheque never arrived. "Sorry we don't have anything on file, can't help you" Lesson learned.

I didn't even know they still did them lol

They still exist so they can advertise a lower price, even though most people won't bother to go through the trouble of submitting them.