A question about 1975 Topps

I was surprised to see that in 1975 for $0.40 and 1 wrapper you could send away for all 24 Team Checklist Cards. I had no idea they did that. Seems like a pretty sweet deal to me. Anyone out there every remember sending in 40 cents and a wrapper for the team cards? Did they do this multiple years? if so, when did they stop? I'm guessing that the team cards could be found in packs as well, so why did they do this? Anyone out there have any answers?

Card Shop Pick-Up: 1975 Topps A's lot (Trade Bait)

I went to an auction today at a card shop in Phoenix. I picked up a nine card lot of 1975 Topps Oakland A's cards. The price was right and I thought I might be able to get something nice for them, so let me know if you're interested in trading for any or all of these. Condition is not great, but it's not horrible either. The other cards I got that are not shown below are Jesus Alou, Glenn Abbott, and Pat Bourque.

A's Team Card

Reggie Jackson

Joe  Rudi

Vida Blue

Sal Bando

World Series Champion Card