Catamaran aircraft carrier was ever proposed? IMO it would be very convinient.
Why there is no one yet?
Probably because, for any given size of ship, you reduce your overall hangar space by at least 1/3 & the width of your hangars by at least 50%. You would require fewer & smaller (thus less capable & shorter ranged) aircraft or a huge increase in the size of your carriers.
If you
do go for a full-width hangar deck, then you have to compensate for the greater mass by making the hulls bigger;
wider = more resistance reducing the speed or requiring larger engines;
deeper = more (though significantly less than above) resistance
but much deeper, (further) limiting the harbours available to you for shelter, repairs, etc.