why is WWE saying there's never been a Undisputed Champion before?

It's acting like that, The WWE thinks the fans don't even remember that. Chris Jericho actually the first Undisputed champion to beat The Face of the wrestling business and The top dogs in the company. That's unpredictable to see Chris Jericho defeating The Rock and Stone Cold Steve Austin on the same night. I bet Triple H will showed a moment when, Chris Jericho had done it. Chris Jericho has been mentioning defeating them on the same night every single night since returning 2007.

I think the WWE is telling a lie because the undisputed championship was active in the WWF/E from December 2001 to August 2002.

It comes down to technicalities.

The WWF/E and WCW world heavyweight championships were unified to create the WWF/E Unified championship (won by Jericho). "Undisputed" was removed from the title's name after it became exclusive to the SmackDown! brand on September 2, 2002, which resulted in the creation of the World Heavyweight Championship for the Raw brand. So the WWE and World Heavyweight Championships have never been unified.

it seems that they forgot about what you just mentioned there.

maybe they're only referring to when after the wwf turned into the wwe, so maybe they're pretending that what happened in the wwf is irrelevant.

they wanna make the match look as special as possible,

what a better way to promote crappy Cena/Orton match than saying "never before!!!!".... typical WWE propaganda, where they actually deny their own history. long story short, WWE is garbage.

so like i said,

it's part of HYPING things up.

WWE is hyping what they are doing now and not what they did 11 years ago.

If anyone would remember that it would be HHH.

That is very true!