Ethernet can carry protocols other than IPv4. IPv6 is one of them, but there were at one time a whole slew of them, like IPX and Appletalk. But ISPs don't carry them, so they're effectively blocked and have largely died out, and everything uses IPv4 or IPv6. Even if you want to use Appletalk today, you encapsulate in IPv4 or IPv6.
There are also a whole bunch of IP transport protocols other than TCP and UDP, but firewalls have a tendency to block them, so today people just encapsulate everything in TCP or UDP.
There are a lot of TCP and UDP ports too, with their own protocols, but those darn firewalls again, so now everything is increasingly using HTTP[S].
The things that get blocked never go away, they're just made to look like whatever is still allowed. Yes sir, Mr. Firewall, this is Hypertext Transfer Protocol over SSL on TCP port 443 using IPv4, which is approved for intercept.
Except that it's really email and games and file downloads and whatever else, with things added daily by everyone on the internet, and no reference for what all of that plaintext is even expected to look like.
So you say you're going to get a DPI classifier and try to distinguish all these different types of HTTP. Except that whatever you exclude will soon be right back encoded as formats and protocols you allowed, because information theory says you can encode anything into anything.
And it gets harder to distinguish them with every iteration, because what you're really using to distinguish them is their encoding inefficiency -- it's the things that are always the same for a given class of data, even though the relevant part of the message is the things that are different. The end state of all of this is that the real entropy is all that's left and there is nothing there to distinguish with anymore.