Why does installing. Gta take 72 hours

Are you able to run a speed test? The game is 73GB in size which isn't small compared to other games so it will take longer than most but the length entirely depends on your network speed.

After you run a speed test, are you hardwired or using wireless? Your local network could slow down depending on your router and or cables being used.

That's not normal at all, and likely has something to do with your internet connection or speed. Are you connected to a strong internet connection? I would check your speed with it because it sounds like it's downloading at a very low speed. I knew someone
who lived out in the country and had very, very slow internet. It would often take him 3 days to download a big AAA game.

gta has a big download and depending on your internet speeds it could take a few hours or days

I would definitely check your internet, if your consoles up to date and your storage on your console. That's what I've done when a game is downloading extremely slow for me.

Hope that helps some. Good luck!

Also, if you are doing other thins on your console an/or internal network it will slow things down causing the install take longer.