Some interconnects between separate organizations are jumbo but those tend to be PNI or secondary vlans. The reason the Internet still runs exclusively on 1500

Some interconnects between separate organizations are jumbo but those tend to be PNI or secondary vlans. The reason the Internet still runs exclusively on 1500 byte IP MTU is that any lower MTU in the path will effectively make the jumbo segments useless. This means any PMTU-D problems customers experience would have been unnecessary and avoidable by just using 1500 everywhere. Many public IX's (peering exchanges) have a jumbo vlan but it's almost always separate from the standard one that only allows 1500 byte MTU.