So I just received an GameCube Platinum from an friend with a couple games, but I realized that the back had only one port, like the regular GameCube. Am I just dumb and after the First Batch of Platinum Gamecubes, they made updates ones? Can anyone just answer why this is?

When the Platinum model was released in 2002, it was marketed as "limited edition." After around a year or two later, Nintendo decided to sell them regularly alongside Black and Indigo. The limited edition bunch (as well as older GameCubes) have the model number DOL-001, as well as the digital AV out port you're looking for. It sounds like you have a second model Platinum GameCube.

It's worth adding that the reason they removed the digital AV was because you had to literally order it off Nintendo's website which costed quite a bit at the time for a cable ($50 IIRC on their website), Nintendo just didn't see the overall benefit I suppose and at the time, it makes sense they went this route.

These days, you can only find the cable off sites like ebay which are second-hand and run up to upwards of $100+ dollars. I've heard there was a project somewhere that was going to make their own special cable for that slot for a much lower price to take advantage of the video quality, not sure what became of that.