I imagine if you only have IPv6 then some parts of the internet will stop working, and customers will then blame the ISP. I can see why ISPs keep the status quo when it probably costs them very little to do so.
I just googled Terraria IPv6 and this is the first result I got:
https://www.reddit.com/r/Terraria/comments/cytn2w/terraria_p...
Yeah, people ask you why you are using IPv6 as if ISP customers get to make that decision...
I just switched to full dual stack (by leasing a static IPv4 address from my provider) to be able to handle incoming connections for my VPN. As long as you don't want to host anything on IPv4, dual stack lite is fine.