Because you can't take that kind of anachronistic view of music.
If Blink 182 never existed and some other band released Enema of the State next week would I like it? No I'd think it's utter shite because I'm 25 and not 12 like I was when Enema actually came out.
Music is not an objective thing, it's all about how it relates to you, the fan, at the point in you hear it and you're right nostalgia is a huge factor. If I heard a Thursday album for the first time I'd wonder who on earth told Geoff he could sing, I'd wonder why TBS lyrics are so ridiculous and pathetic and why Tom Delonge can barely play his instrument but at the time I first heard them those bands connected with me so when you relisten you just revisit the emotions/feelings you got from hearing them back when, even if they'd never have that same effect on you now.
I'm sure there's some people who started loving Blink as a kid who still love Blink and still are mostly into the bands that Blink spawned and that's cool for them, but for me, (and most people on this site given the Vampire Weekend, The National and Kanye West threads receive more hype than any pop punk records) they moved away from three chords and songs about what life is like in high school a long time ago.
So when you listen to a new Blink album there's no nostalgia at all and you're judging the music based on your current tastes. Which I why I think Neighbourhoods sucks, why I don't enjoy any Thursday after A City by the Light Divided, any Alkaline Trio album after Crimson or any TBS album after Where You Want to Be. But play me Tell All Your Friends, Dude Ranch, Full Collapse or From Here to Infirmary and I'll fucking love that shit and sing along to every word like it's 2002 all over again.
I'm aware of that. I would still fall in love with the self-titled, Neighborhoods and DED, though. That kinda shows their target audience rose in amplitude, which means they evolved.
Looking at the bigger picture, they would certainly mean less to me. Like you and millions of other people I grew up listening to blink-182 and their pop punk phase certainly helped a lot...
While my tastes have also changed (couldn't care less about stuff like Radiohead and The National and now they are both top 10 acts for me), I remain totally attached to a core, to a restrictive number of artists (blink, Yellowcard, MCS, JEW, Foo Fighters and NFG to a lesser extent). It's not only nostalgia as I'm able to love their new stuff...
So if someone says this sucks in comparison to the rest of their discography, I can only disagree. It's more a matter of not connecting than of the songs being lazy, worse, etc. If that's the case you simply aren't into the band anymore for any other reason that isn't nostalgia.
Kanye West is also a good example in regards to the "emotional attachment" thing. While I may enjoy him a lot, an artist like him will never be one of my absolute favorites. Because there's just no way I can relate to his lyrics (other than exceptions such as "Runaway") and in the end that's where my love for music comes from. On the other hand, a band like Radiohead feels so universal (like the greatest artists of all-time) that I feel a connection more as a human being than as an individual (blink evokes that)...