Inherited from naval wargaming, where it came about because first rate ships of the line had better armor than second rate etc. so armor class scaled inversely. That meant THAC0 was the best way to figure out what you needed to roll to get a hit.
It’s also not functionally that complicated (your THAC0 minus target AC), just weird and confusing if you try to understand why it works that way.
While everyone has been talking about Baldur’s Gate 3, I decided to cave in and started a replay of Divinity: Original Sin 2. Well, yea, I got a ten years old PC and a Ps4!
I’m sure your PC could run Baldur’s Gate 1 and 2… 😉