The problem (yes, that really should be pluralized, but let's keep this short) with the HHH/Lesnar match is all about the booking. Lesnar makes a big return, LOSES to Cena, then disappears for a few months. Regardless of what they want to storyline shove down our throats, it appears that Lesnar sort of just ran away with his tail between his legs, which isn't going to help sell anyone on his next match.
A bigger point would be that WWE is selling this match to... who, exactly? The younger Cena-era fans either just started watching when Brock was around, or simply have no idea who he is. They saw a guy come back, get beaten by Cena, and then sent his manager out to get beat by a woman. The younger fans, unless they watch UFC, have no reason to give a shit about Lesnar. Let's remember, this guy was last in a WWE ring EIGHT YEARS AGO. In WWE years, that's a lifetime.
The older fans know Lesnar, but they also likely know the backstory and, as you already pointed out, his 'last match'. Between his and HHH's toxic backstage history... well, myke hit on the head, for us it's more about the backstage politics of it, which doesn't inspire me to throw down the (how much is it now?) $50-60.
Sorry for constantly harping on the 'age' point, but it's easy for me to forget. It also sells these kids short on knowing history, but I'd venture that most of these kids knew Lesnar as 'that tattoo guy in WWE12' (gee, talk about not narrowing it down, huh?).