Using mediatraffic's global album chart, Katy hasn't scored a WW #1 album in the last 4 years (=last 208 weeks, so from week 41 in 2010, to week 41 in 2014).

For example, her peers Rihanna and Gaga (who's #1 this week with Grammys2Grammys) have scored three WW #1 albums in that timeframe, so why hasn't Katy (scored a single one)?

Most of her sales are from USA

Because it doesn't matter since there's no official WW chart...

She's a singles artist

Bullying

She is fading

She's a local singles artist.

I'm not into this chart thing but WOW is she a flop?

Uh...because of her sales?

since C2C went #1 WW i'm sure it could outsell Prism which didn't make it to #1
on fair...especially since one has not 1 but 2 legends on it

TD ended with more than LOUD and BTW. PRISM is going to be slightly below UNA, but it will pass ARTPOP, C2C, TTT, etc. easily.

The #1 only matters if you end with more sales.

Currently she is not. She's not really on the charts atm

Because it doesn't matter, hunTy. She is still outselling all of your faves (minus Adele) so who cares.

What a pointless question, sis

We all know her opening sales for Teenage Dream weren't great and PRISM came the same week as a massive K-Pop/J-Pop release that blocked it.
Not that it matters much, the OP proves that having a WW #1 album doesn't secure the kind of album success Katy has enjoyed anyway

because she's not frontloaded like Gaga

Because nobody cares about it, and we already know she is the best pop singer in the industry right now so..